It's not very much time to do much of anything. I think the FBI is just floating that idea since it might seem credible to the average person who hasn't done lab work.
Even assuming growth rates an order of magnitude faster than what happens in live victims, you'd still be talking about 8 hours of time with a bioreactor (not counting set up time). Add to that the 5 hours needed for conversion to spores (that's a biological constraint of anthrax, so there is no way to make that go faster that I know of), and some period of time for drying (let's assume some rapid drying system by blasting it into a tank of hot helium gas via a pressurized nozzle, which might theoretically allow consistent particulate size based on the pressure used and the nozzle geometry), and you're talking about 14 hours minimum.
Under my thesis they were mailed in Florida but most of them got "lost in the mail" and ended up in the back of a truck for several days. They then languished in warehouses for several weeks, and during that period of time "dried out".
Wonder if the FBI othered using a wet preparation and drying it out in postal stamped envelopes. See if they somehow bust it up into a powder.
That simplifies the tale since no machines to dry and pulverize the anthrax would be needed.
How do officials believe Ivins made the anthrax? The FBI says Ivins used his lab to convert anthrax spores into powdered anthrax, but no proof has been presented that he had the equipment or the expertise to do so.
“I’m waiting for it to be shown that the quantity and the quality of the powders in the anthrax letters could have been produced in those suites” at Fort Detrick, said W. Russell Byrne, who retired from Fort Detrick in 2003 and was Ivins’ supervisor from 1998 to 2000. “I don’t know how to make the stuff,” he said.
http://www.baltimoresun.com/news/nation/bal-anthrax0807,0,4430001.story?track=rss