You can assign your time variable to a string, then do a replace on your string to convert the decimal to a colon. Then in your tick timer, you can do an if statement to see if its over 60 to put it back to 0
maybe though take a step back and see how others have implemented this - doing this on tick will be really cpu intensive
I googled in game clock on youtube and found some good tutorials for you
https://www.youtube.com/watch?v=95Up5kmlEkQ https://www.youtube.com/watch?v=9N73RxMHXSg