Compare two time values in ios?

In my app i want to check whether the current time is before or after the time saved in a variable.

like my time1 is time1=@"08:15:12"; and my time2 is time2=@"18:12:8";

so i wanna compare between time1 and time2.Currently these variables are in NSString Format.

Following are the code used to get time,and i dont know how to compare them.

CODE:

        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
        dateFormatter.dateFormat = @"HH:MM:SS";
        [dateFormatter setTimeZone:[NSTimeZone systemTimeZone]];
        NSLog(@"ewetwet%@",[dateFormatter stringFromDate:now]);

Please help me