Dont shoot me but...Dont think Golfs have heated screens, the window button only directs air towards the window only. I have also heard the a/c does not operate when its below 5 degrees, although the light remains lit
Also when your car is cold the air from the blower is cold, thus meaning it takes longer for the screen to clear anyway.
What he said.
The windscreen button turns on the a/c and the blowers on full pelt aimed at the windscreen, however when its 5 deg or below the a/c doesn't come on in order to protect itself.
If you had your a/c on the night before, assuming it was warm enough that it works, this only adds to the problem as all the moisture from the condensor is now being blown at your screen.
If you have to use the a/c, just before you get home turn it off, the heat on high and crack open the window to let the moisture out.
Otherwise as said check the pollen filter. Made a huge difference to me when I changed it, the screen now never steams up unless I've gotten into the car sodden.