The numbers are a bit skewed. The average is roughly 7 months. Unfortunately this numbers includes the homes that are listed 10 to 20k above market value sitting on the market here and expiring.
Homes that are priced within thier range are sitting 2.5 to 3.5 months (mainly the Penn Hills area.)
Jan and Feb sales were up from this time last year even without the tax credit. So if you're priced right you should be OK.