The correct description of the cycle of the air temperature in the office is:
At 7:00 a.m., the temperature begins gradually rising from 65 degrees to 80 degrees, where it stays until 7:00 p.m. Then, the temperature begins gradually dropping from 80 degrees to 65 degrees, where it stays until 7:00 a.m. the following day.
This statement accurately reflects the gradual transitions between the set temperatures and the times they remain constant.