There are too many variables to answer this question with anything that would make real sense - the days on market varies based on the price point of the homes, whether they have basements or not, the size of the homes and their amenities and updates. In some areas smaller homes are selling faster, in other areas larger homes are selling faster. In some areas homes may go under contract quickly, but because they are short sales or foreclosures, they take longer to sell. You should sit down with a local realtor and give them the parameters on the type of home that you are trying to determine ave days on market for.
I will tell you, that home sales have picked up dramatically in the past few months in the Greater St Louis area. We are back to homes selling in a week to a month with multiple contracts if they are fixed up and priced correctly for their area. Buyers are tired of waiting. Many areas of St Louis are back to a 6-7 month supply of homes on the market so we are getting very close to a balanced market (6 months supply is considered balanced)