It shouldn't take long at all. When you arrive at immigration, bear left and head to the connections channel. You'll have a passport check then security screening. Go back upstairs and you're in T2 which then has an airside connection to T1 for Ryanair. From there it's probably a decent 10 minute hike to the FR gates.

I'm going to suggest that even if there are other flights landing at that time, the number of connecting passengers will be relatively small - the vast majority will be terminating at Dublin.