I wrote a controller class that can handle pausing and unpausing timers. You can find it here: https://github.com/LianaChu/LCPausableTimer
It works very similarly to BornCoder's answer. This controller class can be useful if you find yourself needing to pause and unpause timers very often in your project.
If you use it, I would greatly appreciate any comments or feedback like how you used it, what changes you would like to see, or any features you would like me to add. Please don't hesitate to reply with your comments here, or post on the issues tab on the github page.