does anyone know what are the rules regarding the length of time between the RCB and RMAS? presuming I get a positive result from the RCB is it possible to delay entering RMAS for a while - maybe 9 to 12 months?
Yes. Once you have a pass your in! Take for example chaps that pass RCB at 16/17 as a GYC or Army Scholar... Perhaps 5 to 7 years later after Uni Gap year and so on: Welcome to Commissioning Course Blah blah
Your RCB result is valid for 2 years - if you have something you are doing you should be able to ask to defer. I passed in the February and went to sandbags the following January (but that was 12 years ago!). Good luck.