We actually did it one week after baby arrived as we were living in a one bedroom apartment so she had her toddler bed in our room but moved to a two bedroom place just after DD2 was born. Not ideal but just how it ended up working out so it might be a little different as she had never had her own room and we moved apartments at the same time but she was never anything but super excited. We had a sign with her name made up which she seemed to love having on her door and helped her put all her things away. We just spoke really positively about it and how lucky she was to have her own space. She never had any trouble with it, went to sleep in there no problem first night and every night since.

DD1 never even seemed concerned that DD2 'kicked her out of our room' (as DD2 is now in with us), she has never actually demonstrated any jealousy so far. She was 2yr10month at the time and I think we overthought it so much as we were really worried about her adjusting to the baby when if anything, she is tooooo obsessed with DD2 and smoothers her sister with love and attention... 'space' is a very common word around here! It is a good age as you can explain a lot to them, I told DD1 that DD2 was very little so needed lots of milk to grow so had to be close to me even at night because her tummy is very small. I explained that when she had grown she would be able to crawl and play so now DD1 is always keen for DD2 to feed or sleep because she wants her to be bigger!