You're wasting your time if you're lifting weights for OCS.
That's interesting because I rarely ever did a pushup or any other bodyweight exercises yet I was one of the most physically prepared guys in my OCS platoon. I did spend a fair amount of time in the gym though.
It may not be completely necessary, but it will help to a large degree when combined with moderate running. And it's far from being a waste of time.
To the original poster, go check out T-Nation.com. They have a great deal of legit lifting, conditioning, dieting, etc... type articles.