Sure. I've always taken the approach that a woman has to hang around for two years before I figure she's serious about a relationship. I wouldn't dream about marrying anybody until some time after that milestone (and it certain is no guarantee of success, as I've been divorced), so I'd offer that as a suitable sort of approach to merging two families.
There are going to be lots of expectations that only come to light after much time, so provide the time to find out what they are, how they conflict, and how to negotiate solutions. I'd certainly wait until long after the NRE is gone to think about changing living situations.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.