Hi,
Instruction is non-public transport flying (no AOC required). Therefore shouldn't interfere with rules on flight time limitation. So flying 900 hrs for Ryanair shouldn't preclude doing some instruction in your spare time - legally anyway.
However, if you have the energy to do any extra flying (above 900/year) with sufficient rest between the two is another matter! I would give it six months at Ryanair to see how you do.
This is my understanding of the rules, I of course stand to be corrected.
L.