Definitely be ready exactly when your window opens and hit Savi's first then. I had my pick of times for Droid Depot. Oga's was another tough one, too. My entire week there were only two time slots when my window opened.
My window for dining opens tomorrow morning (3 night stay in June). Savi's, however, won't open until Midnight tomorrow night. I'm anxious. I did Savi's in March, and now DD (my observer before) really wants to do it herself (newly-minted Star Wars fan she is!).
I'm going to try tomorrow night at midnight for the afternoon/evening of 6/19 and then the next night at midnight for any time on 6/20.