It sounds like you are using ANSYS mechanical for a thermal analysis and not Fluent or CFX. This is the fluid board, and you may want to post over there to get a better answer. These fluid packages could solve for the thermal temperatures in the body and the flow field. Obviously, if you just need the temperature in the body this is a bit of an overkill. What are the boundary condition you actually have?
There is a nice Mechanical thermal analysis example in one of the Innovation courses (it involves radiation, but the model building is the same). I recommended you look at that. Keep in mind that if you are modeling the air domain in your model, you won't actually see any fluid moving.
But to answer your question directly, click on Analysis Settings in the tree. In the details panel change the end step time. You can also specify the interval you want to solve at.
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