A countdown timer turns time, which can feel abstract with ADHD, into something you can see. That visibility creates gentle urgency and a clear boundary: you are not committing to finish the whole project, only to work until the timer runs out. Lowering the commitment is often exactly what makes starting possible.
It also gives you a clean container for one task, a natural point to take a break before fatigue sets in, and a record of what you actually did, which is satisfying and motivating. Pair it with a distraction-free setup and it becomes a simple, reliable focus aid.
This is general information, not medical advice.