Save a Day Every Day. Tip #4: Remove float and lag

There has been a little lag between me publishing Tip #3, and this article on removing float and lag. This is coincidental only.  The fourth tip in my series on how to save a project day every day is to remove float and lag from your plan. That’s a really broad statement. After all, by eliminating it all you will find your entire project is all a big critical path. That’s not what I’m recommending.

Just for some review, so far in this series, I’ve recommended 3 other tips: make sure your plan is clean and good, make sure your estimates are accurate, and ensure your status is correct.

First off, what are float and lag?

• Free Float (FF) on an activity is the time it can be late in finishing without impacting the start of a following activity. Activities on the critical path have FF = 0. Activities that have zero float must start on time and finish on time to prevent the schedule from slipping. In the following diagram, the red activities are the critical path, and have a FF=0. The blue activities are not on the critical path. They have FF=2 and FF=3.
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• Total Float (TF) on an activity is the time it can be late in finishing without impacting the end date of the project (even though some tasks may be rescheduled). Sometimes this is also called “slack”. Continuing on the previous example, the TF for the first blue activity is 2+3 = 5.
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• Lag is time that is added to the relationships between activities to force a delay between activities, or trigger an early start of an activity. To that end, lag values can be positive numbers to account for things like concrete curing or delivery of an ordered item, or negative numbers to kick off an activity before the predecessor is finished such as with lead time to start a preparation of an activity like getting painters ready before the dry-walling is finished. In the following diagram, the second activity has a lag, based on the Finish-to-Start activity of the first activity, plus five days. During that five days of lag “nothing” happens. (But there’s a reason for it, like supply chain delivery time, paint drying, etc.)
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If you review your schedule, and filter for float and lag, you’ll start to find lots of available time in your plan. But wait, before you get all excited about eliminating that float and lag, you need to understand it and the opportunities that may lie within it. For instance:

• Is there lag time that you really need and can’t get around? For example, if you need time for the concrete to cure, ensure you have the right amount of lag in your schedule and don’t let anyone walk on the wet concrete. Maintain accurate lag where you need it.
• Can you benefit from float by using it to negotiate more favorable contracts or deliveries? If you can give a contractor or supplier more flexibility in the schedule, they may be able to schedule other activities around your project and provide you with higher quality people or deliverables, and / or cheaper delivery.

Once you’ve carefully considered the importance and value of lag and float in your schedule, now you can start focusing on lag and float in order to save a project day.

Lag on the critical path

Focus on activities on the critical path that have a “mandated delay” and see if you can reduce that delay. For example, you might have lag because you have to wait for something like a part or specific person to arrive. Who owns that? Start working with the person who is responsible for the lag and see what you can do to reduce it. For example, if you are waiting for materials to be delivered to site look for ways to get the material completed and delivered more quickly such as using influence (contractual or squeaky wheel) with a supplier to prioritize your materials on the production line, find another supplier, or use “hot-shot” delivery services for some items. When you do this, balance out the value of reducing the lag with the cost of expediting.  For example an alternative to reducing the lag might be to assign a “waiting” work team to other non-critical activities.

Float off the critical path

Presumably activities that have float aren’t on your critical path and consequently eliminating that float won’t save you project. But, as a project ebbs and flows, you will find that activities that aren’t on the critical path today can suddenly show up on the critical path. Simple message here … don’t waste an opportunity to look at activities that are nearly on the critical path. These might be activities with only a few days of float. Go after these vigorously to keep them moving along so that they don’t surprise everyone and end up on the critical path.

To do this, you will work with your project team to tune estimates (See Tip #2) of your work packages and also to reorganize the last-minute details of the schedule to be more efficient. This is done using Short-Interval Planning methods like WorkFace Planning or Advanced Work Packaging, and Lean Construction (a.k.a.) Last Planner. Team supervisors that are involved in short-interval planning can use the float to manage their work within the constraint of not impacting others. Make sure your project teams are aware of the importance of completing activities that aren’t on the critical path.

To find activities that are off the critical path, but could end up on it, you might have your scheduling solution calculate multiple critical float paths (sequences of activities). This will identify the most critical path and sub-critical paths that affect the completion of the most critical path.

Eliminate negative lag

This was discussed in Tip #1. “Ensure your plan is technically correct.” Negative is caused by intentionally scheduling an activity to start earlier than a traditional finish-to-start relationship would drive. Don’t do this.

Eliminate negative float

Negative float is caused by imposing an unrealistic finish date or must-start and must-finish constraints that can’t be achieved within the critical path of the project. Imagine you have three activities that must happen in lock-step, and each takes 3 days. It’s Monday right now, and the project owner wants you to be done by Friday of this week. Not possible. (A piece of advice, never say that. Consider your options and see if anything can be done to collapse your schedule.) I’m sure you get the idea on this one. You need to do some time travel and start that project early in the preceding week. There’s your negative float. You are behind schedule before you even start.

Eliminate the negative float by moving your project’s finish date out and eliminating constraints. Do this in an educated and methodical approach.

Manage resources

Float gives you the opportunity to manage time as a resource. With knowledge of your available float you can choose to move people and equipment among activities that have float and reallocate those to activities on (or very near to) the critical path. To that end, in this tactic, you look for opportunities to bring resources from an activity with float to an activity with little or no float. You would only move resources around if adding additional resources is efficient (e.g. you can’t put the dry-wallers, painters, and electricians all together in the same space at the same time).

Crash your Schedule

Crashing means that you add more people and equipment to a given activity in order to complete it faster. This is related to managing resources, but is subtly different. The previous point relates to managing finite resources and reallocating them to critical activities (leaving your project costs approximately the same).

Crashing can mean that you bring more people onto the project or have existing resources work more. This causes an increase to project costs.

You can’t crash every activity. For example, if you have a small space and one painter, adding a second painter to the mix will probably just result in one painter painting, while the other one watches and waits for a break in the action so that he can get a few brush strokes in. Similarly, if there is a training curve to an activity, you may actually slow progress down by introducing more resources to it.

Fast-track your Schedule

Fast-tracking means that you look for opportunities to save time by taking activities that are ideally done in series (one after another), and looking for ways to overlap them, or do them in parallel at the same time. This can’t and won’t work for all activities (e.g. drywalling, painting, and electrical won’t work, but plumbing and electrical at the same time could work).

Fast-tracking introduces an element of risk. After all, the activities were scheduled in series for a reason and to reduce the risks. Risks of fast-tracking can include worker conflicts and / or space conflict (which may result in more serious problems), and poor quality (which could result in rework).

Here are some links to good articles about using float and lag and applying some of the strategies discussed above:

• Understanding the basics of CPM calculations, by Scott W. Kramer and James L. Jenkins
• Save time and money on projects by using float, by Sydney F. Love
• Do more with less, by Malcolm Wheatley
• Critical path, or chain, or both? by Tammo T. Wilkens, PMP
• Mission critical by Patricia Lira Mogollón,
• Evaluation of projects using critical path analysis and earned value in combination, by John W. Brown
• Sleepless in Seattle? Avoid the scheduling nightmares, by Jeff Nielsen

Summary – How will removing float and lag help you save a day?

By focusing on your projects constraints, relationships, and resources, you can remove float and lag from your schedule and save a day. You can find opportunities to do this with some basic filters in your schedule to help you find some obvious things like negative lag and also multiple critical float paths. Beyond that you are going to call on your project team-mates to look for solutions like opportunities to tune the estimates and work-order for work packages, crash and fast-track, and to lean on suppliers to deliver sooner. Removing float and lag is a team sport, and it will help you to bring your project in sooner.

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Full disclosure – I’m the General Manager, Western Canada at Western Principles. I help my customers find the value in enhanced project and portfolio management solutions to optimize their return on their projects.

Western Principles provides consulting services for Microsoft Project, UMT360, our own project-centric applications, and other solutions.

The views and opinions expressed in this article are mine and do not necessarily reflect the official policy or position of Western Principles.

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