I wore weave for six months when my hair was NL. I took it out every two months, and I only relaxed once during that time period and I had a ton of NG. I estimate that my hair grew 3-4 inches past SL.
I must caution you though - Make sure they are gentle with your hair when they wash your weave. Also, I think you should allow the professional to take it out, and unlike some other LHCF'ers who are much more hair savvy than me, I let them relax it immediately. There was no way I could even contemplate dealing with all that NG. Anyway, my only mistake was that before I could open my mouth, the stylist started chopping me up. I have learned as a result of this to tell them your demands up front (i.e. "I'm doing this to grow my hair," "Please do not cut my hair once it's relaxed," etc.)