This sounds a bit weird! Is the time correct when you set out in the morning, and only incorrect when you reach work?
There are a couple of ideas that occur to me that you could try.
Most radios that have an RDS radio will operate with the CT (clock time) function of RDS. The CDX-GT29 certainly has this. If CT is switched to 'ON' then the time displayed by your radio will depend on the information being broadcast by whatever station you're tuned in to. You don't say what you're listening to but it could be that the station is broadcasting poor information (even if you're listening to a CD the radio will still be tuned to something so could still be a problem). If you are tuned to a national station like the BBC, then I'd be surprised if this was the issue, but if you're tuned to a smaller, perhaps local broadcaster, then this might be the problem. In this case you could try switching the CT function to OFF and then setting the clock manually and see if it hangs on to the correct time. To do this, press and hold down the 'select' button until you enter the setup mode. Then press the 'select' button repeatedly until the CT setting is displayed - you toggle between ON or OFF by turning the control knob. When you've set this to whichever setting you want, hold down the 'select' button again to exit the setup mode.
The only other thing that might be happening is if you don't have a permanent battery connection to your car. All Sony radios have a red and a yellow power supply wire to connect to your car. The yellow wire should always be connected to a permanent supply, in other words one that always has 12 volts regardless of whether the car's ignition is on or off. This holds the radio's memories such as radio presets and clock time. If this isn't connected correctly (i.e. switches off when the ignition is off) then whilst it won't do any harm, the clock would keep resetting. Just a thought.
Anyway, hope one of these ideas might be of some help!
This morning when I went for work, again time was correct and then half way there it was set to arround midnight and then when I arrived at work ... the time was 15:45 .o0(Great time to head home again)
I'll try the CT function... and get back with an update