Guesses on how long a junior FO would take to make RJ CA are virtually impossible at this point. So many factors are involved, its really not even worth trying. Back in the day of the AVRO, there were some RJ FO's that bypassed the SAAB all together and went straight to AVRO CA. I believe they had to wait about 7 years to do this.
That was then, this is now... RJ85FO gave you some golden advice. The future of XJ is uncertain at best. Get some CA time under you belt when you can. The Saab is a fine aircraft. Everyone at XJ has flown it for some period of time... we generally don't have a lot of tolerance here for PreMadonnas.