Timer - how to only start it when I need to

This is for a live training. I pose the question to the trainees which will take a minute or two, and then I give them 3 minutes in their groups to discuss. I hid the timer and then made it appear with a button. That did work except that the timer had already been ticking down during the time that it wasn't visible.

Any ideas on how to get it to not count until I tell it to? (I do realize I can have it on the next slide, but wanted to know if I could accomplish this on the same slide).

Thank you,

Tanya