I just got some cornrows done on Feb 28. I just took them out over the weekend and will be putting them back in today. My hair growth was alot more noticeable over the 3 or so weeks since I wasn't bothered w/ combing it. I'd go for it if I were you. I will be kepping mine in for another month and think I will do them again through the month of June. If you have baby hairs and are somewhat tenderheaded like me, you can just tell them not to pull from the very edges. HTH
There's a picture of the one's from Feb in my hair album.