I want some help

[HritikR]

How to use timer even after app closed

I want to use timer like even when application is shutdown (closed). I have a timer of 2hrs and the timer will only works when/until I stay on that particular screen and when I press back (way to another screen) then timer not works Whereas I want to use that timer for 2hrs even when app closed. Please help to fix it, How to achieve that? Please reply with blocks image if possible. Thanks!