Most likely, you will go to SERE before the RAG. Everyone in my class did, and personally I think that is the way to go. Typically any waiting you do in corpus is between your final check and your winging ( I waited about 6 weeks), then the week after your winging you will detach and report to VP-30 student control. If you have SERE prior to starting 30, you will basically show up to StuCon say hello get a SERE packet with some instructions your travel itinerary and then told that they will see you when you get back. I would recommend doing SERE before the RAG and here are a few reasons.
1. Assuming you are an ensign and might make jg before you finish 30, being a lower rank is better at SERE. (it will suck either way, but lower rank = slightly (very) less suck, but anything can help)
2. There is something that happens at the RAG, when you get towards the end that is satisfying that you are finally going to a 'real' squadron to do your job for real that lends itself to wanting to get started. Not to mention dealing with a more in depth PCS move across the country, maybe an imminent deployment (some of my class will leave for deployment one week after reporting to their squadrons, others will meet their squadron on deployment) and I promise that you will not want to finish SERE one day and be packing for deployment the next.
3. Most important, just get it over with. You have to do it, you know you have to do it, it is not going away, and you will think the whole time at the RAG that you still have to do it. I promise they will not forget, so get it over with and move on. You can use your time at 30 to heal your emotional wounds...ha.
I hope that helps, if you need any other info let me know.