This is a practical application of the
rule of three.
You have a timer that goes from 0 to 60, and you want to represent that in a bar that goes from 0 to 100. So you apply the rule like this:
If 60 (your max original value) is translated to 100 (the max progressbar value), then original value X is translated to X*100/60. (check it. For example, If X is 30, it should give 50 in the bar)
EDIT: Also, what timwil says with less words