NSCalendar *calendar = [NSCalendar currentCalendar];
NSDateComponents *comp1 = [calendar components: NSHourCalendarUnit | NSMinuteCalendarUnit
fromDate: date1];
NSDateComponents *comp2 = [calendar components: NSHourCalendarUnit | NSMinuteCalendarUnit
fromDate: date2];
Now you have all the data you need to compare the two dates.
comp1.hour > comp2.hour
comp1.minute > comp2.minute