how would I use NSDate's dateTimeIntervalSinceNow method to calculate the difference between today and an NSDate sometime in the future?
The examples I have seen all take arguments such as the number of seconds:
NSDate *date = [NSDate dateWithTimeIntervalSinceNow:60*60*24*3];
NSDate *date = NSDate dateWithTimeIntervalSinceNow:(NSDate*)futureDate];
As suggested by Dan in his comment,
[futureDate timeIntervalSinceNow] accomplishes the task.