Do you have a score table (with durations shown) or something?
If "yes" it's better to use precise numbers and show time as it was suggested by @JohnGB
But if it's just for users own information and you can drop, for example, seconds for durations longer than 15 minutes and minutes for durations longer than day, and let user see approximate time I believe you may use something like this:
"Duration: 42 mins", or "Duration: 5 mins 16 seconds", or "Duration: 33 hours", etc.
I believe that if you don't have a score table where user could compare values you may drop seconds or a minutes sometimes without any harm since user will not remember exact time from the previous try, but just a more meaningful part of duration, like, "last time it took 5 hours 20 mins and now just a 3 hours and 10 mins", etc. And if you have a duration table I think that you should show a part of it so user will be able to compare his or her time with previous tries.