The timetable is showing Cork - Galway via Dublin at 3 hours. Allow an hour for checking in on the Cork side and getting to where you want to go in Galway and it's four hours.
The return trip, direct, is half an hour, so the total trip time is 5 and a half hours (again allowing an hour returning for checkin and Cork side travel). That makes it half an hour faster than driving, assuming you're not driving at rush hour, which could add half an hour in Limerick alone, not to mind Ennis....
Can't believe Ryanair are stopping the 6.45 to Dublin, it's always full when i travel on it, and it's a brilliant time. You can be in Dublin city centre by 8, do your thing and get the 13.30 home with RE.