Contraction rule of thumb? -- help!

Hannah
So I've been having very mild contractions since about 4, it's now 10:21, and they're starting to get a little more intense then just the noticeable crampy feeling bh ones. I just started timing them, but should I wait till they hurt? Or become really uncomfortable? I am so nervous about having my baby in the car or something.. Third time mom, but first time actually having to track contractions. Help!!!!! Just give me the typical guidelines to follow. Should they be a certain length for them to count? For how long? I just need some reassurance please-- thanks.