XC70 - 2001 V70XC - Autodimming Rear view mirror

Hello all.

Have a little problem with the rautodimming ear view mirror in my 2001
V70XC. It doesn't work too well or too fast. My wife has a Acura TSX
and the mirror in that car changes within 2 to 4 seconds of it sensing
light from behind. My Volvo's take almost 30secs to 1 min before it
changes.

1. Is there a way to diagnose the mirror separately?
2. Is there a sensor to be replaced?
3. Can I get a replacement mirror and install it my self?
4. How much (app.) would a new one cost from Volvo?

Thanks all for the help.

GGO in NYC.