This app was mentioned in 4 comments, with an average of 2.25 upvotes
I use an app called stamina manager, it works for other games too. You have to manually enter your current/max stamina though.
https://play.google.com/store/apps/details?id=jp.gr.java_conf.naktak_app.gamestamina
I think it's possible to make an app that could poll your account via one-time-code but I don't have time to work on it.
bro, 6 mins is common sense these days. Arknights, Priconne, World Flipper, you name it, all of them are 1/6min.
Also, Arknights have a love events that don't require stamina, like CC and if you are playing annihi, you will be "playing" for way more than 20 mins lol.
Anyway, I was googling to make sure the AP regen rate was also 6 mins and saw your post, had to comment lol.
Since most of the games have their notification broken and don't really tell when your stamina is full I recommend downloading one called Stamina Manager by NaT APP. You can register multiple games there to notify you when you stamina reaches the desired amount.
That is why I use this.
I use this app for Stamina/NRJ Management for my games :
https://play.google.com/store/apps/details?id=jp.gr.java_conf.naktak_app.gamestamina
(don't worry, the app is also in english)