Just a small utility I wrote for personal use which I thought I'd share in case anyone else finds it useful. As the title says, you set which audio app you want to stop after a set period of time, simple as that.
I personally use it before I go to sleep with either Umano or Pocket Casts, both have sleep timers but I find this much quicker to setup and use. Plus it has a lower volume option so it can tune it down to silence rather then just abruptly stopping the music.
Play Store Link
Any issues let me know, otherwise enjoy