Sixty seconds
Everything else here asks you to pick something. This does not.
60
Press start. It runs by itself. Follow along or do not.
Four things in one minute: two slow breaths, stand up, a sip of water, and let your eyes look at something further away than a screen. None of it is impressive. That is the point.
It runs offline once the page has loaded, so it still works with the plane mode on. Nothing is stored and nothing is counted, so stopping halfway costs you nothing.