Timer is reset because you are restarting it in "On start of layout" event.
There are several alternative and easier solutions:
1. I see you've added Persist behavior to the text object. It will ensure that the Timer continues to run after layout is restarted, but you need to add "Timer is NOT running" condition to the first event, to prevent it from resetting.
2. Instead of Persist behavior, you can make the text Global. It will have the same effect, but you need to be aware that global objects are not destroyed when you switch to another layout.
3. You can do this without Timer behavior - add this event:
int(TimerVariable)%12=0
Trigger Once
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