Life is soo unpredictable, so why do we make predictable timetables and to-do lists? This is a fact you should keep in mind when planning or scheduling. Which is why based on my experience, I always advise that you should leave spaces/blocks for those external factors when planning your day (always). There is a concept in business studies called 'prudence'. I'd explain it with respect to time management: 'when faced with uncertainties, overstate your time allocation'. In simple terms, give spaces for the effect of external factors when planning. Allow breaks in between and tag them 'miscellaneous'. Such that your actual schedule is not disrupted.

Clear communication with all the stakeholders is critical. Sometimes external factors will derail your timeline if you didn't build in any slack. Which is why building in slack isn't a bad idea! But if you don't have any, look at the priorities on the project. You may be able to still complete the important tasks without going too far outside the timeline. If not, then you may need to rearrange the schedule. Or if you have other team members you can pull in to help play catch up, make sure their schedules are cleared to join the project. Clear communication with the stakeholders is critical. The last thing you want is to hit the deadline without completion and surprise everyone with an unfinished project.

To handle unforeseen factors affecting your project schedule, assess the impact, adjust plans, and reprioritize tasks. Communicate openly with stakeholders, involve your team for solutions, and use contingencies or seek external help if needed. Stay adaptable, proactive, and collaborative to keep the project on track.