Here is a good link to keep bookmarked regarding spots:
http://www.fhainfo.com/condos.htm
I am assuming that if the property is not already FHA approved, which is why you are requesting a spot approval, then chances are that the percentage of units that FHA loans is 0%.
I'm in the process of one right now, and generally speaking, so long as the property adheres to all the guidelines, the overall process shouldn't take more than a week or two.