I rarely get out of 'Ohana in less than 90 minutes - and I usually dine solo.
I also rarely get into the restaurant exactly on time; usually I get seated somewhere between 10 and 20 minutes after my ADR time.
Basically, you will be wolfing your food to make it to the Poly marina by 8pm.
If you can't get an earlier ressie, make sure you tell your server that you're in a hurry and why, so that they will get your food to your table quickly.