Additional Schedule Refresh Times

I have only just been learning about scheduled refresh and when I try to add in a time for schedule a refresh, there are a limited options - On the hour (00) and on the half hour (30)

We need some flexibility - could this something like the following times be added i.e. (15) / (45) etc.

The logic/reasoning behind this is due to the
- timing of the refreshing of where we source our data from
- timing of the number of reports which are being refreshed - so we can stagger them a bit better rather than a number of them all being at 00 / 30.