To make it easy comparing two NSDate instances in Swift we can overload <=, >=, >, < and == operators with NSDate types on left and right hand sides of overloading functions. timeIntervalSince1970 is a safe measure for comparing most dates. I used timeIntervalSince1970 to make the decision if two dates are equal, less or greater.
Note that operator overloading declarations should be placed in global context. I highly recommend documenting this behavior in your developer guide documents.
With those operator overloading declarations in place, now we can compare dates with ease: