The normal procedure at Ryanair, (if there is such a thing!) is to complete one winter in the right hand seat, it depends how many hours you have when you join Ryanair. Then, as long as you have kept yourself out of trouble, you will enter the command upgrade program. This is subject to you passing the upgrade interview and have demostrated that you have the correct competencies to command a 737 to FR standards. And believe me not everyone makes the grade, despite what you might read on pprune!
I was flying with a DEC last year who flew the Dash-8, including the Q400, and had around 6000hrs on the type. No problem upgrading to the left seat of the 737.
Hope that helps a little.