Oh? Here's the chart of Ivins' overtime hours:
It looks to me like Ivins overtime hours were unusual, and they happened at exactly the time that the anthrax mailer would have been working on the attack anthrax.
It also isn't really that much overtime. Even in September, the month with the most number of o/t hours spent in BSL3, that's only 1-2 hours per day. Or it could include a couple of weekend days. Those kinds of hours are nothing unusual for a scientist. Scientists do not have predictable 9-5 schedules; their work hours can vary widely depending on their project.
The other thing is that the o/t started in August, not September--which would mean that if he were, in fact, preparing anthrax, he would have had to know about 9/11 before it happened. Which I find rather hard to believe, because none of our intelligence agencies whose job it is to try to find out stuff like that knew, and Ivins was just an ordinary citizen.
Looking at PubMed, I see that Dr. Ivins published in Apr 2001, Sept 2001, and Jan 2002. Hmm. Just maybe, those BSL3 hours were spent generating data for those papers (all of which discussed an anthrax vaccine).