In California, general practice (for those who managed to find a BigLaw job out of school and are not clerking) is that you:
July: Take the Bar
Sept/Oct: Start your job
November: Get your Bar Results.
In the past, firms would usually let you fail the Bar once and re-take in February without firing you. Now the rumor is they won't be quite so patient.
From my understanding, the above is pretty standard no matter what state you are in. Feel free to correct my if I am wrong.
I qualified my statement because the dates people take the bar and the dates they receive results vary. I believe some states get back to you as early as October or as late as December, and the Bar exam itself may be taken in July or August. But the general pattern holds at all major firms I know of.
I'd also like to add that if for whatever reason you don't get a job straight out of law school, firms generally won't hire you until you have received your bar results. So, for example, those who had offers at Heller Ehrman who did not re-interview this season will have to wait until November (at the earliest) before they can even interview for jobs, instead of getting the extra 2 months or so of work in before results are received. And if they fail the bar, they'll have to wait another 6 months.