Treat deadlines like they’re real, because for somebody down the line they are.

A deadline rarely belongs only to you. Somebody further down the line has planned their own day around receiving the thing, and when it slips they absorb the cost without having had any part in the delay. That is why private flexibility about dates has public consequences. Keeping to the time is a way of taking other people seriously.

Find out who is actually waiting on your next deadline and what they do when it lands. If you are going to be late, tell them as soon as you know rather than at the deadline. Then build your schedule to finish a day ahead of theirs.