Been though this a while back;
Here was my problem:
I wanted to have a constant reminder after every 2.5 hours, each and every day.
Used few apps, found one that worked, at least for a few days... started spiraling down...
Started missing the reminders (i guess it was blocked by "do not disturb" that i soldem forget to disable). I even whitelisted the app to bypass any android blockages ( could be that i missed a few, idk). The app just couldn't work,
Ended up using the inbuilt alarm on my phone, added 2.5 hrs from the hour that i wake up, every day (0500hrs) and set them all as alarm ( yeah, each and every one after incrementing 2.5h) upto the time i probably get to bed (2230hrs)
With a same custom subtle low-key ringtone on all of them.
Or use the brain power to conjure up a prank of the century