When a doctor says: "Do this for 30min every 2 hours." What do you do?

Do you do that thing for thirty minutes then do it again after two hours, or after one and a half?

Like if you started at 10 o'clock

Schedule one (the thing's time counts as the 2h)

10:00-10:30 — do the thing 10:30-12:00 — wait 12:00-12:30 — do the thing

and so on so on

Schedule two (the things time doesn't count as the 2h)

10:00-10:30 — do the thing 10:30-12:30 — wait 12:30-13:00 — do the thing

and so on so on

Which schedule do you use and is there a correct one?