I don't know this is perfect solution. But this will work
NSDateFormatter *df = [[NSDateFormatter alloc] init];
[df setDateFormat:@"mm:ss"];
NSDate *date = [df dateFromString:@"00:00"];
NSDate *date1 = [df dateFromString:@"00:24"];
NSDate *date2 = [df dateFromString:@"00:07"];
NSTimeInterval interval1 = [date1 timeIntervalSinceDate:date];
NSTimeInterval interval2 = [date2 timeIntervalSinceDate:date];
NSDate *addedDate = [date dateByAddingTimeInterval:interval1+interval2];
NSString *resultDate = [df stringFromDate:addedDate];
Hope this helps.