To solve the problem I applied the procedure suggested by CISCO to reset the phone. Once done, phones were showing the correct date and time.
Below is the procedure suggested:
Step 1
Unplug the phone:
If using PoE, unplug the LAN cable.
If using the power cube, unplug the power cube.
Step 2
Wait 5 seconds.
Step 3
Press and hold # and plug the phone back in.
Step 4
When the phone boots up, the headset button, the speaker button, and the mute button light up. When the light on the Mute button turns off, press 123456789*0# in sequence.
When you press 1, the lights on the headset button turns off. The light on the Select button flashes when a button is pressed.
After you press these buttons, the phone goes through the factory reset process.
If you press the buttons out of sequence, the phone powers on normally.
Caution
Do not power down the phone until it completes the factory reset process, and the main screen appears.
