I'm an FMG, and I intend to take Step 3 within this year. I am aware that unlike Step 1 & 2, the examinee can't choose his/her dates. Roughly how much time before my intended date should I submit my application, and how much time do they usually take to decide which date to give you? For e.g., if I want a date in August. when should I submit my forms?

I submited my application at the and of February.Received permit March 3,was assigned to the period 03/03/09-06/30/09.It lasted about one-tow weeks to get permit after application submition dates.So I think if you planning to take it in August,better to submit application now.
Good luck

I phoned FSMB's Examination Services department directly (817-868-4041). They said when you send in your application.. it will take 1-2 weeks for your application to be fully processed and be assigned your eligibility period. and another 1 week after that to be issued your electronic scheduling permit. So therefore you should apply 3-4 weeks before the start of your desired eligibility period. your eligibility period is 90 days. You should use the Candidate website to monitor the status of your application and the availability of your scheduling permit and score report. https://apps.nbme.org/fsmbexamstatus/prod/jsp/login.jsp

all the information required to apply can be found at http://www.fsmb.org/m_usmlestep3.html