Yes, air temperature can affect the cooking efficiency of a solar oven, because some of the energy that goes into heating your oven will be lost to the surrounding air. Depending on how much energy you lose, it will change the efficiency of your solar oven.

When figuring out the efficiency of an oven, you have to think about where the energy goes. If you use a solar oven on a hot day and then use the same oven on a cold day, I would expect that on the cold day the oven will lose more heat to the colder air. However, if your oven is well-insulated, the heat loss will be less significant.