ADHD time blindness is a documented perceptual difference: the brain cannot reliably feel how long a task will take, how much time has passed, or when a future deadline will actually arrive. The result is chronic underestimation of task cost, wildly missed deadlines, and the two-time-zones problem (now vs not-now). This guide covers the neurological mechanism, five early signs, and five external-cue strategies (visible timers, anchored routines, count-up sprints, pre-committed first actions, hard stops) that give an ADHD brain the temporal scaffolding it does not produce internally.