First thing in the morning after her last night in a cot.
I'm a great believer in keeping children in cots as long as possible. I think putting a toddler in a bed too early can lead to all sorts of problems, so all of mine have been at least two and a half before being put in a bed. Emma has been in her cot bed since she was about seven months old. She has always been tiny, so she was in the Moses basket in our bedroom until then. She has always been quite happy in her cot and has never made any attempt to climb out of it, so I just left her in it. However, she couldn't stay in there forever, so one of Emma's birthday presents was to have the bars taken off her cot.
She thought it was wonderful when she walked into her room and was able to climb in and out of bed by herself. She immediately invited Lily into bed with her and Lily read her a story, which they both enjoyed. At bedtime she climbed happily into bed, but as she lay there drinking her milk she looked around her room and said "Put the sticks back on."
She had no trouble going to sleep after her busy day and slept right through the night (this is still quite unusual unfortunately). The following morning Lily came to me and said "Emma is awake. I just heard her little footsteps running across the floor". We went in together to find Emma sat on the chair in her room playing with her toys!
This seems to be the way of things now. She gets into bed at bedtime, stays there until morning and then gets out of bed and plays in her room until someone comes to get her. It has been a smooth transition for her, I believe because I waited until she was that little bit older before doing it. I have to admit to being a bit sad that all of my children are in beds now!