I would do it for 1 hour prior to the Wishes scheduled, once they release the hours and times. If you really want to see Wishes you need to get there a bit earlier and request a window seat to view it and be willing to wait. We didn't request any, and could not see anything from our seats, and becuase of how the restaurant is laid out, we had to walk around the restaurant and bend over to view it. After 2 minutes of that, i decided it wasn't worth the trouble =)
Just a head's up =) You'll enjoy Ohanas - we loved it!