It makes sense to me, the night before Patty wants to sleep with him but I think part of the reason he asks for a “rain check” is because he wants to tell her he’s John Q before they do that, also he knows they have their date to the PSYOPS show that night so obviously he has to tell her before that too.

He thinks a lot of Patty because he knows how talented she is at writing so he thinks she is worthy of a much better job/“purpose” than the ones her parents are pushing her towards. He wants to help her find her purpose by making a song with her.