Yes, we've always had a 'set' time of going in to get DD. It's usually been about 6:30 as that's when she most naturally wakes. We were more lenient however, when she was teething and struggling with sleep more in general.
We now have a version of the Gro-Clock, that switches from a sleeping bunny to a bunny that's up and walking to school at 6:30 am. DD knows that we won't come to get her before the bunny wakes up, and it works quite well. Sometimes she sleeps through it and sometimes she's up a while before. This morning I heard her a little after 6 am; by about 6:25, I could hear her saying, "Wake up, Bunny. C'mon, wake up!!"
LOL!!