If the flight times change then you won - now you have a flexible ticket that you can chose to use or not to use up to the departure. If you decide not to travel you can allways get refund. If you decide to travel only then you accept a shedulle change.
I am not sure how Ryanair 'flight credits' work. You can get them instead of a refund. Is it posible to use them on any departure on the same route or only on flights costing the same?