Tia

Are you asking if you can be put on a "wait list" if a spot is not available for a particular character meal during your trip and then called if/when a spot opens up?

If that is your question... then the answer is no.
The best bet is still to call 180 days out and try early and often.

when i really want an ADR, I call 3x a day every day. most of the time it's effective, sometimes it's not. sometimes i know not to even try (for example, i was making ADRs 2 weeks out, CM's is booked solid, i know it's not going to open up for me).

with character meals in mind specifically, as CRT and PSB penalize for no-shows, if i want one of those, i'd really start checking when the cancellation policies kick in, which are 24 and 48 hours respectively i believe.