I only played Shaiya casually and got level 26 on my fighter in about 2 days. But once I found 20-30 PvP I got addicted and stayed there until level 30. After I got use to the PvP by rank 3 I started grinding again. In about 2-3 days casual playing got to 40 then I got bored and quit.

But I believe if you play casually you should be able to get 50 in 1-2 weeks. I personally did not skip that many quests. If you play a guardian/defender or mage you should be able to get 50 much faster.