To compare two dates we use compare:
- (NSComparisonResult)compare:(NSDate *)anotherDate
compare Returns an NSComparisonResult value that indicates the temporal ordering of the receiver and another given date.
The date with which to compare the receiver. This value must not be nil. If the value is nil, the behavior is undefined and may change in future versions of Mac OS X.
The receiver and anotherDate are exactly equal to each other,
The receiver is later in time than anotherDate,
The receiver is earlier in time than anotherDate,