Like Allee mentioned, the temps should stabilize after a number of hours.
Make sure, if you use the above lighting, that you check the temps several times in this 12 hour period as you don't want the temps to be over the 96-97 degrees. If it is, move the light farther away.
Also, realize that under the tank heat is better for young leos and that you will need a cool area as well as the warm area in the tank.