Dear customer, I apologize for my delay to get back to you.
I see two queries in your question, the first is with reference to the time system, i observed that you have been without the navigation system for several years and it seems to me that the clock of the dashboard works according to the time zone that the system perceives. That is why it is normal that over time when the navigation system is out of date the vehicle loses the time and therefore cannot reset it correctly. Then it is a problem with the firmware, or you have to check it throught the sat nav to set well the clock/time.
So the first thing you have to do is update the navigation system software again, there is another problem that is when the vehicle turns off and the clock seems to restart, that is when you can manually set the time but when you turn off and start the vehicle It is now deconfigured, so you have to see and verify the fuses because the fuse is responsible for maintaining energy in the console, if it has burned the electrical systems are completely turned off when the vehicle is turned off and this causes the clock to reset again each time you turn off and turn on the vehicle.
On the other hand, as a second consultation, I see that you have a problem from time to time when starting the car that sometimes does not start, so I would like to know how long you have without replacing the vehicle battery, because apparently you have a charging problem in which you should wait for the electrical system to charge properly to be able to start, so the vehicle sometimes starts sometimes you must wait a few moments for the electrical system to grab a good load and turn on when the battery voltage is low.
The relation where the two problems are related is when the battery has voltage problems, the electrical systems fail and cannot be configured or cannot be restored as the problem that you present in the clock.