Just out of curiosity, can you go to the bar and order a milkshake at the 50s Prime Time Cafe if you don't have a reservation? I'd really like another one of their PB&J milkshakes, but I don't really want to eat there on this trip.
I have never tried the PB&J shake at 50's Prime Time but I am definitely going to this trip!! We have dinner ADR's there one night but I'm going to go to the bar and get a shake to go on a day we're not stuffed to the gills.
Not positive about ordering a TS credit at the bar, but it seems like you would be able to. But you can definitely get the milkshakes as a dessert: menu.
Sounds like a good way to try their food without running the risk of being teased, I just would cringe if I got teased like some people have reported being teased.