Recently, my 1999 Lexus 300 resets the clock to 1AM each time the engine is off (overnite). I can reset the clock and it works fine if I am driving. However, if I park it for work (8 hrs) or overnite, it reads 1AM again when I start it up.
Does it read 1am before you turn the key to start, or only after. If only after, then you most likely need to replace your car battery.
Check the fuses.
+1 - The Lexus clock logic is programmed to reset before the battery voltage drops enough to stop cranking the engine.