When you set a URL you can choose the refresh time. However when you want to change that, I don't know how, so I've tried going in to Change Provider and choosing Custom URL, not inputting a new URL, clicking the dropdown for the time, and selecting the EPG that was already being used from the Pick Existing list. No idea if this changes the time to refresh though.
Also, I have old EPG's showing up in the list and can't seem to remove them?