Jeezo, I didn't realize my relationship with my husband would be quite this picked apart in order to justify my opinion. If there is a specific appropriate time limit in place for getting married and establishing a family, none of us - DH's exW included - got that memo. I will bet several of you haven't either. 
To clear up my history, since so many are curious, DH and his ex separated about 6-7 months before I ever met him. Which is to say that he and I met 6-7 months after she got fed up with the marriage and she moved out of their home, and moved into the home of the man who is now conveniently her partner. That all went down when DSD was about three. A few weeks after mummy moved out, the 50/50 arrangement was established and DSD was going between her old home with daddy and mummy's new home, spending time with mummy and her new "flatmate".
I met DSD when she was 4.5, just after she'd started P1, about five months after DH and I had started seeing each other. The relationship had reached a point where either we were serious about each other or we weren't, and if I was serious, would I please finally meet his daughter and stop making him live a split existence. I know other people don't reach that point in five months, but we did. The one nice thing about having a serious relationship or two tank, is that you have a much better idea of what you want from the next one and don't faff around when you finally find it.
I started doing overnights at DH's flat with DSD in November 2010, got engaged in December 2010, moved in Feb 2011 after DH sold his flat (the sale of flat being part of the separation/divorce agreement), and married my husband last August. Meanwhile, the 50/50 arrangement has been maintained, so my stepdaughter has been very much a part of my relationship with DH. He is not Uncle Dad.
As many of you will be aware, in Scotland, you must be officially separated for about a year in the event of irreconcilable differences before you can proceed to court for a divorce. And given that lawyers cost a fair bit (I'm sure you're familiar with this part too), it can take several months to have the means to consult a legal advisor, negotiate with your ex-spouse, and finally sign a separation agreement. So although DH and exW separated when DSD was three, they did not finish splitting up the contents of the flat, selling the flat, moving house or many of other unpleasant tasks that take place during a divorce, until just before DSD's fifth birthday.
I have not been in DSD's life for long, but I have been there for quite a few important events. None of the time I've put in may be of any importance to the adults on this board, but I am not insignificant to her. The child has tried to call me "mum" on occasion, and I have had to discourage that.
ExW has further explained since yesterday that she thinks DSD's Xmas would be ruined if she didn't see her father on the very day - that she'd be missing him too much and be upset. I disagree with that - I think she is quite used to waiting a few days to see Dad or Mum again, and happy to have Santa Claus arrive at a few different houses over a few different days. But I don't see what goes on in the other house, or hear what DSD says. We've all agreed to disagree for now.
Heaven's sake.