Is it safe for me to relax my hair?

I don't want to over-process my hair and make me bald... You see, I previously relaxed my hair already. My hair type would be around the medium. I kept the relaxer inside my hair for only a estimated 9 minutes thinking that would be enough. How foolish of me not performing a strand test before I've done this, was my first time. Anyways, to sum up the question. The hair isn't straight, some of the wavyness was removed, but its still a little wavy. Wondering if its safe to commit to another relaxation process? If so, how much time do you reccomend? Probably 5-6? What? I have no idea. HELP!! To remind you my hair type is about medium and the last relaxtion was 'round 9 minutes long.. There is no breakage going on. No skin conditions, etc. So yup...help..