If a recipe calls for grilling boneless chicken thighs, how long should they be baked?

I would brown them on the stove top and if you must put them in the oven insert a remote thermometer and leave them only until it reaches 160 degrees.

If you are choosing to bake them over grilling them, the time could really depend on your oven. I would bake them at 350 degrees F for 20 minutes to start, and then check on them every 5 minutes. They can go from underdone to overdone very quickly.

I may be going out on a limb here but I believe if the recipe calls for grilled boneless chicken thighs there is absolutely no baking involved.