If your TM-D710 is more than 5-8 years old, your time on the radio head display may no longer work. This indicates the lithium battery powering the radio head clock has expired. Here's the easy fix.
1. Order a replacement Sanyo ML614 lithium battery. They are available on Amazon, eBay and other battery outlet stores like Batteries+, for about $8-10. Good luck finding one in a brick&mortar store. They'll likely have to order it in.
2. When the battery arrives and you are ready to restore time on the TM-D710 display, remove any cables from the display and place it on your work area. You will need a small phillips head screwdriver to complete the repair.
3. Remove the two screws at the back bottom of the radio head and set them aside.
4. Pull the back off the radio head and set it aside.
5. You will see the battery and mount on the left side of the display. Remove and discard the old battery. Install the new battery.
6. Replace the cover and re-attach the two screws to the radio head.
7. Re-attach any cables and mount the radio head back in its normal location.
8. Apply power to the radio and go to the AUX display (FUNC + left knob push). Select Menu 524 and change the date, then select Menu 525 and change the time to the correct settings. ESC to return to the operating display, which should now indicate the correct time.
That's it. It took longer to write these instructions than it did to fix the radio head time display.
Dave K7GPS