Well, why use Date over TimeInterval in any case then? Date is really just a typed wrapper over a TimeInterval, which is a typedef Double. The only reason Date exists is to give meaning to some specific Doubles (timestamps) and not let Calendar APIs affect all Doubles.
So, yes, this can be done with TimeInterval directly without issues, and then a map on the result will give the same result as doing stride on Date directly, but why not allow it?