The lack of this feature makes the new Email Program appear much more complicated for us. My use case is simple geographic timezones. I can't send to New York, London, Munich, Australia and Los Angeles all at the same time; I need to stagger them by timezone.
I might try the Email Program once and see how complicated it is to do multiples, my concern is we're going to clutter things up and add a bunch of extra work for the very minor benefit of being able to see stats by timezone.