I've found it takes a pretty fair amount of sun. I did some tests years ago trying to make wooden canoe racks for my truck. The epoxy did not stand up well over the long haul but did last a year. that was in direct sun, no garage, for a year. I think a cup or bowl inside where some of the UV is blocked by the window and you probably only get early morning or late evening sun, would last a long time.
My only user goblets were finished with wipe on poly. We only use them once a year and then wash them out. They are still like new.