If the others suggested aren’t quite right for you, you might try looking for an interval timer app. These are generally used for fitness, but it seems to me that type of setup might do exactly what you want if you just set up a “workout” that has a single 30 min interval and repeats.
I typed in the url and… yeah, that was A LOT of boobs and butts.
Came back here to see that I mistyped the url. Doubling the “O” results in many boobs and butts.