Your time concept is misconstrued, lvl 20 takes 8 hrs, rng means that raid readiness could be another 5 mins or 2 weeks (that's farming marks which takes maybe 10 hrs a week to cap so let's say 20 for those with absolutely no luck) now you're 28 and raid gear rng means you could have a full set in 45 mins or run the raid 3 times a week on normal and hard or hard only depending on what you group you find. So min you are looking at 20hrs of game play maximum you could end up like me running 3 raids on hard a week with no 30s to show for it.