This app was mentioned in 9 comments, with an average of 1.44 upvotes
I use ClearLock and it works great for this. It's the best I've found simply because it forces you to reboot your phone to turn it off. There are other options that are super easy to stop, but I almost never feel like rebooting my phone unless it's an emergency.
Another vote for clearfocus, make sure you install their other app too, it'll allow you to basically prevent distracting apps from running for the duration of the pomodoro. Very VERY helpful.
https://play.google.com/store/apps/details?id=com.clearproductivity.clearlock&hl=en
The runner up app is Clockwork Tomato
https://play.google.com/store/apps/details?id=net.phlam.android.clockworktomato&hl=en
Good, very customizable, has metrics you can look at . Nice widget
Check out Clear Lock
Is something like what you're looking for?
https://play.google.com/store/apps/details?id=com.clearproductivity.clearlock
Clear Lock I think you mean something like this