FYI, somewhere I found some info on the White Labs' brett vials. Apparently they have 50 million cells per mL and they're 35 mL, so they're 1.75 billion cells per vial. This is less than 2% of a normal yeast vial. Can someone else confirm this?
I pitched two into a 1 L starter and it took about 5-6 days to complete, so with only 1 vial, I'll bet it will take yours another day or two...and you still won't have enough yeast for a normal pitch rate. If the Mr Malty and Wyeast calculators are right, then 1 vial in 1.2 L will only give about 29B cells when done, which would be a very low pitch rate for a normal beer.
I've done two all brett beers and both times I used WL. I pitched two vials into a 0.6 to 1 L starter, then pitched that into another 1 L starter, in an effort to get to a normal ale pitch rate. A lower pitch rate might be OK with brett, but I didn't want to wait forever for it to complete. Both of these beers reached 85% attenuation and FG in about 1 month.