We did it at 9 weeks. Was wonderful!! I would leave her for 10 seconds if that!! It was really just teaching her that her cot was for bed. To this day (2.5) she only sleeps in her cot, which is fantastic, and also knows she isn't allowed get up once she's in there. That was my main aim, and the sleeping came with it, within a few nights. I did spend some nights in there patting her for a long time, but NOt getting her up again was the main thing, so patting her for an hour or so was not a problem .xxo