After your post only seeing that my gif post was marked as solution.. well, post#15 marked as solution? Well it have no relation with topic or query I think..
I just shared my view, may be even more simple way we can short it and if I come to know let me share it
This is not a solution (because it continues counting after restarting the app).
Another open question would be what should happen to the timer if Screen1 is no longer visible, eg the home button was pressed. I would assume that the count should not continue, but only as long as Screen1 is visible (i.e. in the foreground). Questions over questions...