It is indoors, but I do think time of day can certainly set a different tone for the ride. On one hand it is very cool going at night because Pandora is INSANELY awesome at night and that flows nicely into the rides darker indoor setting. On the other hand, there is something cool about going during the day because inside the ride it feels VERY different than the sunny FL day outside.
Either way, I HIGHLY recommend visiting Pandora during the day first thing in the morning and then going back the same night, when its good and dark, to get the full experience of how it changes.