I was in a similar situation to you a few months ago. It took me approximately 3.5 weeks from level cap to get into SoO normal. That was with a lot of help though from friends and I bought all the 553 boes as well. that said, 3 weeks into SoO and im 551 now. You definitely have time to gear up and get into it. As far as the legendary quest goes, It will take you about 11 weeks or so to complete.