//Gives us the current date
NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *components = [gregorian components:NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit fromDate:[NSDate date]];
[components setHour:5];
NSDate * date = [gregorian dateFromComponents:components];
[gregorian release];
Что-то в этом роде должно сработать.