You could finagle it in Google Calendar. It's a bit of a hack, but it'll work. You basically need to set up 3 events to cover the time frame since you're limited to 6 notifications(5 early + 1 at time). Then set those to repeat indefinitely.

So you'd set the first for 11 am with notifications starting at 5 hours earlier. Next would be 5 pm. Final would be at 9 pm.

It's a kludge, but it gets the job done.

Try MyTherapy. Yes, I know it's a medication reminder app.

HabitBull is fantastic

This is probably overkill, but if you can't find an app that'll do what you want, this would be pretty easy to set up in tasker or macro droid. I have something similar but more complex set up for myriad medication reminders

I use 2:

https://play.google.com/store/apps/details?id=com.bleyl.recurrence

https://play.google.com/store/apps/details?id=metu.mobi.aareminder

I use Tasks.org for short term reminders, and use Proton Calendar for long term reminders, and ones that repeat from period to period such as birthdays

What about using a dedicated calendar in the calendar app of your choice, set up events with reminder for every hour and repeat those events everyday ? You could then dismiss the notification once the task is complete.

I don't want alarm. It's to annoying.

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.

Worked ever since 😊