CMX2 zoned to CMX2.5

[Chelsea Downs]

Hi Everyone, I've been a long time reader and finally decided to join. I'm pretty new at this third property. 

I'm considering a cmx2 which needs medium rehab, and is currently 1 level but could go up two stories by right. The issue is there would me much more value if I could get it rezoned as a cmx 2.5 has anyone done this? How long did it take? How much should I expect?