My usual security time at DFW is about 5 minutes or less, maybe 10 on a Monday morning. It rarely gets longer than that except for holiday weekends. When you exit security, just have a quick look at the line to make sure it's not abnormally long.

BTW, there's very little outside security at DFW, in the way of bars, restaurants, or even comfy chairs. Consensus is, the best place for this sort of meet-up is the Hyatt hotel at Terminal D. Check the South forum for a recent thread on this topic.