You knew the deadline. It was on the calendar. And somehow it still arrived like an ambush, going from "plenty of time" to "due tomorrow" with nothing in between. If this keeps happening, you are not careless. You are experiencing time blindness, one of the most common and least understood parts of ADHD.
Time blindness means the future does not feel real in the way the present does. A task due in nine days and a task due in two hours register at roughly the same emotional volume, which is to say almost none, until the deadline is close enough to trigger panic. By then your options have shrunk.
Why "later" is one undifferentiated blob
For a lot of ADHD brains there are really only two times: now and not now. Everything that is not now gets filed into the same vague bucket, so a thing due Friday and a thing due next month feel equally distant. The result is that you cannot pace yourself, because the runway is invisible until you are almost off the end of it.
Willpower does not fix this, and neither does a longer to-do list. What helps is making time concrete: turning "soon" into a specific day that will actually come find you, instead of a feeling you have to keep re-checking against your own unreliable internal clock.
Let the deadline come to you
The fix is to stop relying on noticing. Give each commitment a real date, and let the system surface it at the moment it needs your attention, with enough lead time to act rather than scramble. A task that quietly raises its hand a few days before it is due gives you back the runway that time blindness hides.
The goal is not to feel time more accurately by trying harder. It is to offload the timing to something that does not have time blindness, so the right thing shows up on the right day whether or not you remembered it was coming.
ADHD Notes surfaces what is due, what is overdue, and what you asked to see again, at the top of your day. See how it works.