I tossed together a quick free app that will run on anything Windows10 (phone/tablet/PC/etc). Pretty simple just ability to set delay before beep, multiple different par times, a counter of runs, etc. The only kind of advanced part is it uses voice synthesizer and speech recognition (backup buttons in case of issues). So it will as "Are you ready", wait for you to say "ready", then say "standby" and wait random or set delay before beep, then pars. Then repeat until you want to quit.
Works well with cordless Bluetooth headsets/earbuds so wife doesn't have to hear all the beeps/noise/etc to keep me out of trouble
https://www.microsoft.com/en-us/store/p/dry-fire-timer/9n0979m8n7ph