It is probably an indicator of a larger issue. I don't recall if it resets to 12:00 or just stops incrementing (if no battery for 10 minutes, it is then 10 minutes slow) because I know my different vehicles behave differently.
It probably isn't a low power or a draw but completely losing power.
It could be specific to the clock (you don't mention what vehicle or year), could be in the radio (do you lose presets), digital below the radio, analog (Town Car), etc.
00 Grand Marquis LS Premium - 97 Cougar 4.6 Sport - 89 Cougar LS - 63 Falcon 302 - 82 F-150 - 97 Mark VIII LSC - 2017 Escape SE - 2012 Fusion Sport AWD