The interval_type property is not included in the array of returned targets objects. To me, this suggests that the target timeframe will be a blanket setting across all categories.
Good that it’s already got some support in place for it though, just needs a interval_type per targets object. Making that change may be understandably more difficult in practice than explained.
UPDATE
Also, @anon50039658 has recently agreed custom timeframes for holidays is a good idea…
… so the same feature could be applied to all categories.