How to use the online timer
Twenty minutes gives a sleep-focused practice room to work. The first several minutes are usually taken up with the mind running through the day, which happens to almost everyone and is not a sign the practice is failing; what follows the settling is the part that matters. This is deliberately different from a daytime sit, where the aim is alert awareness. Here the aim is drowsiness, and any technique that sharpens attention is working against it.
Lying down suits it, which is the opposite of the usual advice. A slow body scan, moving attention from the feet upwards, or breathing where the out-breath is noticeably longer than the in-breath, both pull in the right direction. Dim the room and let it be on the cool side beforehand, since the body drops its core temperature as it falls asleep and a warm bedroom works against that.
Falling asleep partway through is a success rather than a failure, which makes this the one timed practice you are not expected to finish. If the mind keeps returning to tomorrow's list, writing the list down before lying down removes most of its urgency. If it keeps circling anyway after a good while, getting up and reading somewhere dim for a bit is more productive than lying there negotiating.
Common questions
What position should I be in for this?
Lie down, which is the opposite of the usual advice. The aim here is drowsiness rather than alert awareness, so anything that sharpens attention works against it.
Does it matter if I fall asleep partway through?
Not at all. This is the one timed practice you are not expected to finish, and falling asleep is the outcome rather than a failure.