If you've got an experienced person to make cooking fires, it won't be totally exhausting. If not... figure it will take 1-2 weeks worth of practice to get to the point where you can reliably get a fire going and have it be as hot as you intended. As a novice, figure it will take at least 2 hours to get the fire to do what you planned, even if it's just boil water. Experienced and in practice seems to cut it down to about an hour if you're starting from scratch... and on tour you'll definitely be starting from scratch. Add an extra hour or two for green or wet wood.

After spending a week camping and doing open fire cooking... I'm planning to buy a little stove. I won't say never again, because I had fun and learned a lot. But there's a lot of skill and practice involved, and it is much harder manual labor than most restaurant style cooking. (unless for some reason your restaurant's kitchen is habitually moving around 20 gallon stockpots every hour or so, or doing multiple whole animal roasts per day)