I'm not sure why you are splitting it into two separate variables for min and sec.
This is counting up in hours/mins, but you could use the same principle:
[System | every 1 second] > [time.var | set value to "time var + 1"]
[text] > [set text to | zeropad(int(time.var/3600% 60)) & ":" & zeropad(int(time.var/60% 60))]
Also, by this way, just make the 'time.var' a global variable and then you can use it across all layouts.