You can really start rushing anytime. It doesn’t hurt to reach out to units and ask about visiting or when they’re holding a rush event, as for applying, I’ve heard guys apply even if they don’t have a complete packet (degree complete, AFOQT scores, etc) that way they see your name and know you’re interested. My viper unit hired a home grown avionics troop who applied 6 times and 4 of the times he wasn’t eligible but they knew he was interested and that’s exactly what I’m going to do even though I have quite a bit of school left. That’s just my opinion though.