JABoa writes (in part):

Then, his problem is to decide whether any additional gain outweighs the diminution of the exclusion if he waits beyond those 9 months.

I reply:

If I understand the facts correctly, the exclusion isn't "diminished" in 9 months; it disappears entirely because the poster will no longer have used the house as his or her principal residence for 2 of the last 5 years. I do not believe this requirement can be pro rated. --Bob