I’m not entirely sure what you are trying to do, but you can create an NSDate object by adding time in seconds on to another NSDate using:
- (id)dateByAddingTimeInterval:(NSTimeInterval)seconds
// eg. to add 8 hours to current time:
NSDate *mydate = [NSDate date];
NSTimeInterval secondsInEightHours = 8 * 60 * 60;
NSDate *dateEightHoursAhead = [mydate dateByAddingTimeInterval:secondsInEightHours];