Timer that starts, stops and continues whenever I like it to

I'm currently into doing so-called "Line Distribution" videos - example here​​ - for K-Pop music and I'm a bit clueless right now...

As seen in the video, there's a timer that counts up for the duration the singer Hwasa sings her first part (at 0:16) and then stops when she finishes singing (at 0:20). It continues to count up when she sings her second part (at 0:28) and again stops (at 0:31) when she finishes singing it. Same with the other members.

Initially, I've experimented with Premiere Pro's standard timecode, but that didn't gave me desired results. I can't really tell the timecode to stop at a certain point and resume where it stopped to continue counting - just like in the video above. Which leads me to... After Effects! Thanks to Rick Gerard​​, I stumbled across Dan Ebberts's Expressioneering Design Guide​​. However, I never played that much with Expressions before... I mean it works, but now what? How can I tell it to start, stop and resume whenever I like it to?

Any ideas/suggestions/tipps?

Regards,

Maurice