The time required will vary according to the type of oven you have and the time of day you cook. Most dishes take about the same time as a conventional oven once your oven reaches operating temperature. Preparing your dinner in the morning instead of the evening. You'll go home and eat while your friends go home and cook. All it takes is some practice.
Solar ovens are great for camping or at the beach.
They use no flame and can be used in fire restricted areas. It was a great event, about 60 solar ovens in a cooking contest. The problem was that only judges got to taste all the great food. This is when my brain got in gear. Zap, we should organize an event with other solar applications included and have a BIG potluck dinner at day's end for everyone to share.