The meal itself typically lasts about an hour, but 'Ohana is notorious for having long waits for a table, even with a reservation. 'Ohana is one of the most popular restaurants on property, so there is often a logjam at the podium and in the lounge area. I would reserve 30 minutes in your itinerary to wait to be seated.
We were there on good Friday and the place was packed! We only waited about 5 minutes for our table and were in and out in under 1 1/2 hour. There were six of us - 3 adults, 3 kids...everyone agreed it was one of the best meals of the trip!!!
We have always had to wait to be seated at Ohana. Even when the place was only about half full. My guess would be that on average the wait is about 20 minutes past ADR time. We always plan to be at a TS meal for 90 minutes minimum. I do find that breakfast tends to be a little bit faster.
Ohana was the most rushed meal of our trip...they had us in and out within 45 minutes...it was crazy...the salad, bread, potstickers and wings came out....then no more than 5 minutes later the noodles and broccoli...and then the flood of meats! We asked twice for more potstickers - these came out after we were done...and then dessert was on the table before we knew it. Whew...even typing this took almost as long as my dinner at Ohanas!