We have just started using one with out almost 3yo DD1. I set it for her normal waking time the first night and when she woke earlier I went in and said 'it's still sleeping time, the cow is sleeping' she then went back to sleep and woke 5 mins after her clock would have shown morning. I changed it to 5 minutes later the next few nights and she slept until 20mins before it 'woke' so I told her to go back to sleep until the cow woke up - she dozed on and off but didn't call us until the cow woke up. I will leave it at the current time (6.45) for a few days then change it to 6.50 and move it up 5 mins until 7 am which is deemed sensible in our house!
Thanks so much, we've been on holiday so not had chance to try out the clock. Now we're back, DD is ill so it's still in the box. Going to get it going as soon as we're back to normal and although she can't get out of the cot, I hope to 'train' her to at least entertain herself or go back to sleep.