I have a repeating group which returns dates, the data source is in date ranges but there isn’t an option to sort by date so the group ends up out of order. Any ideas?

You can’t, in vanilla Bubble, sort date ranges.
Yeah so what you’ll need to do is create your own custom “Date” field (or whatever you want to call it) as part of your Schedule data type and use that as your sorting field.
Though, I think I meant to mention that this can be done with List Shifter’s SORT action.