How does an enlisted Soldier go about applying for OCS?

Sir, at what point would you say that it would be appropriate to approach them? 6 months or so at the unit?

SPC (Join to see) - I would give them time to know your abilities. At some point, your PL should set down in a counseling session with you to discuss with you your performance, what schools you need, and what your goals and his goals are for you. That would be a good as time as any to get the ball rolling.
Things move differently now. When I was enlisted, the Army was going through a major expansion (the Reagan Years), so my battalion would come through about once a year and solicit any soldier that had a degree and high enough ASVAB score, and their commander would recommend them, to go to OCS. The second time around I said yes.
I will tell you that OCS is an entirely different kind of suck than Infantry OSUT. After the initial shock, if you had your head wired on correctly, I felt the Drills were doing their best to see that you succeeded in the Army. I never felt that same about OCS TAC Officers (the Officer Equivalent of a Drill Sgt. to a degree). Just think of it as the test you need to endure to reach your goals.

SPC (Join to see) - Going a bit further, if this is your goal, apply when you feel ready. I liked being in a Rifle Squad, so I stayed a couple of years before deciding to give OCS a try. Now for the Downside of being an Officer. You will never be as close to a bunch of guys as you were in OSUT or should be in your present squad. Your job as an Officer means being able to make decisions about those guys future that may not be what they want and you have to be willing to make decisions that can put them in harms way. The Officer world is competitive, you will seldom get as close to any of your fellow officers as you are with the guys in your Squad and Platoon.

Thanks Sergeant