How to set a timer of 2 hours and even if the application is turned off, it continues counting

What I want to do is put a button that when you activate it starts a countdown of 2 hours and that when you close the application or continue in it but on another screen it continues counting. Also that when the counter ends, it sends you a notification and that when you enter the application it is shown as if it has already finished.
What I want to do is something like clash royale chests that open in a while even if the app is not there.

I hope I have expressed myself well, otherwise ask me if you have any questions about what I want to do.
Thank you.

What have you tried so far? Show your relevant blocks etc.

My idea rather is to make a screen where my game currency can be mined and thus obtain more game currencies.
Here I leave the aia for you to review:
Miner.aia (6.7 KB)

We need to see your relevant blocks, not an aia file.

what about doing a search in the community?

to send a notification at a specific time also when the app is closed I can offer my alarmmanager extension…