An object X is placed in thermal contact with a large thermal reservoir Y whose temperature remains constant. The temperature of X is recorded every 5min:
Time after contact (min): 0, 5, 10, 15, 20, 25, 30
TX(∘C): 80, 70, 62, 57, 54, 53, 53
Determine the earliest recorded time at which it is reasonable to conclude that object X has reached thermal equilibrium with reservoir Y. Justify your answer using the data.