@massivelyop it depends, cos I've played games where I've gone from zero to endgame ready in like 3 days, and other games where it takes 8 to 16 months to scratch endgame.
I feel like if it's going to be more like a modern western mmo, I shouldn't take more than two weeks to be endgame ready. Older eastern mmos on the other hand? Preferably 5 months, but it really depends on what catchup mechanics you have in place.