There is no native way to 'pause' a timer, you will need to assign the timer handle to a variable, and keep track of the round time yourself. When you need to pause it, you delete/kill the timer, then when you start it again, create the timer again and subtract whatever time has passed since you first started it + the amount of time since pausing it.
Alternatively, you could have a repeating timer at a 1.0 second interval and manually subtract the time from within the timer callback, when it's in a 'paused' state, don't subtract the time and exit the function. Once the time variable you have set hits 0, run whatever code you need.
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