At least he won't be Old Wayne for some time yet, he just doesn't know how the flow of time might work here after everything else that's happened to him so far. That will be an interesting, and likely distressing revelation for most others involved when he becomes Wayne-colored goop for a while.

Just to be safe, when he gets that slip, he quickly correlates the symbols to the buttons, and is relieved when they're easy enough to match. He presses close to that slot and murmurs a quick "thank you" before straightening up and moving to punch in the offered code. The moment it confirms, he's going to dip into the room and hopefully not spot anything any more out of place than just the fact that Pal was in a cell to begin with.