Time Element with Javascript

Hello fellow Heroes!

I am attempting to push user data to php and wanted to know how I could also include the elapsed slide or scene time in minutes and seconds (00:00) format as opposed to milliseconds. I know there was some sort of formula to this but Javascript is not my langauge!

Also, is there a way to stop the timer at the conclusion of an exercise and have it continue from the time it left off once the user starts the next exercise (next slide or scene)?

I have attached screenshots of the code I used for the timer and the code that was provided to push to php.

Thank You,

Chris