I cannot find any regulation on this, so how far out can active duty who are separating from the military apply for federal service jobs?

I think you can apply whenever you see the job posting, but I don't think you can start work until you've separated. For instance on all the job postings I submitted, one of the main questions was "When do you start Terminal Leave" and "When is your EAS date". Because I took a full 2 months of Terminal, I was available to work right away.

Staff, there is no regulation on when you can start applying. I would say start applying 6 to 8 months from separation.

It would depend, if you are applying for a federal job and you have 6 months to go it may be enough time, and it may be too much depending how the HR section handling your packet works. It is not uncommon to hear of people taking 6-months to a year. and three months is fast.

Your S1 should help. But a 4187 for early release on account of a job offer, signed off by your chain of command should help facilitate it.

I used to be a senior hiring manager on the Fed side. What you've heard is correct. You don't have to wait and 6 months out is a good thing, usually. One year is an eternity in the HR world so that's a bit long. Your availability date needs to be in your package on USA Jobs. This is great for the open continuous announcements. However, for positions that need to be filled soonest, don't expect them to wait around for you. I have seen some wait for specialized positions, i.e. a certain kind of chemist, etc. but for most series, the pressure is to fill because you have work to do and you don't want to roll the dice hoping to avoid the next hiring freeze. Besides the freeze, shifting caps because some other office in the organization mucked up their staffing and other anomalies means a position here to fill today can be gone tomorrow.

Don't foregt to rewrite your resume for each position you apply for. One resume won't work as it has to be crafted to meet the specific requirement mentioned in the announcement. I would not apply 6-8 months out as it only takes 3-4 months to get hired and working. Semper Fi!

You could look in AR 635-200 and see if it mentions anything about applying for federal jobs. I don't think it does but I am pretty sure you can apply for a federal job at any time, you can also start working a federal job while you are still on transition leave. However, you cannot work while you are on Permissive TDY. I doubt anyone really monitors your activities once you sign out on your last leave and run back to the unit and say "I seen Joe Snuffy working at the FBI today".

I think it should be safe to say that if you know you are separating , 6-12 month is when I would start looking.