Datetime. It also provides sorting. It also provides intervals which sounds like what you're interested in.

Less applicable to the question but more important, imho, is that it handles all the nasty edgecases that any developer who didn't write Datetime shouldn't be bothered to know about handling dates and times. This would include the situations when a minute can have 59 seconds, 61 seconds, and even 62 seconds. (Yes, those situations do exist in really odd circumstances, but it would suck if you accidentally ran into one of them, right?)