I just started out as poly recently myself. My new relationship is shy of 2 weeks old, so I am coming from a place of NRE.
My guy and I decided to make our fourth lunch date include my husband, and then hubby went back to work while we spent the rest of the day snuggling at the park. I met his wife yesterday. So, it has been quick for us, but he thought it was important so we both knew that the other wasn't cheating. That said, both of our partners are feeling extreme compersion and just as much happiness, so they were open to meet us. If my DH had been struggling with fear and jealousy, I don't think I would have done introductions so quickly.
We don't have any rules - neither spouse has veto power, so it was all good.