I have granted lvls from my lvl 60's and up, you do not loose them til your time is up. My last group was 2 druids that I only lvl'd to 23 and had no time to do more. I granted them lvls I had on my hunters, locks, and shaman, all above lvl 60 getting them to as close as I could to lvl 61 without hitting it. One kill after that, my druids hit lvl 61.