parachutes,

Do you notice the time error AFTER you shut down your computer?

Once you shut down the system, take note of the time.
Later on when you boot up, note the time again.

See if the difference on the clock matches the time that has actually elapsed.

If so, it is a sign of an aging internal battery.

You can obtain a replacement and if your handy with a screwdriver…can replace it yourself.

;D