Not the OP, but I used to work at a retail job where we couldn't touch our phones or have them out visible. There was no clock around either so having my phone speak the time aloud from my pocket every 30 minutes helped me get through the day until the shift ended.

Also automating this would remove the element of imperfect human functioning. If you had to open up your phone and press snooze every 30 minutes, that takes a few seconds or minutes if you're busy, and then the timer would start to lag behind and no longer be in sync with a clock's time and thus lose its utility. And how exhausting would it be to keep on top of that task for 16 hours every single day without any mistakes allowed ever? My ADHD brain is getting anxiety just thinking about managing that.