I though it was timebased when I saw 0 to 59
So, depending on some event, the counter will be updated, right?
Do you intend to update only one counter and reflect the change in the other?
Do you know in advance which counter will be updated first?
Maybe the MapRange node is a solution.
Value: {current value of counter 1}
InRangeA: 0
InRangeB: 15
OutRangeA: 0
OutRangeB:59
→ you set the return value to counter 2.
or
Value: {current value of counter 2}
InRangeA: 0
InRangeB: 59
OutRangeA: 0
OutRangeB:15
→ you set the return value to counter 1.
The Floor Node can be used against the return value if you need strict integers.