We went when DS was 11 weeks, and it was the perfect time for us because I was about to go off the deep end and he managed to learn to self-settle. However, I think it was very, very early for that to happen.
I think somewhere in the range of 4-6 months would be ideal. You have a baby who has a tummy that's a little bigger so is more likely to cope with feeding every three hours, your baby can develop sleep associations, your baby won't be standing up or trying to crawl in the cot (hopefully)...
Why don't you give them a call to ask what they think?