Cancel and rebook ADR question

[jdelay]

To qualify for free dining I need to cancel two days and rebook as a room only for those two days. I Think that means my Royal Table reservation will be cancelled automatically.
Does anyone know how quickly the cancellation shows up on the Disney computer so I can rebook for the same time?

 

[distherapy]

I canceled a room reservation to use a better discount last year and none of my dining reservations were affected.

But just as an FYI - I canceled a dining reservation and grabbed it again in minutes online.