Thus far, it's always worked best if we meet before anything happens-ie, the same day they meet face to face for the first time-if they met online, or the first time they are going to meet "out of context" from where they met (if they met at work for example).
Now-that's not to say that we "go over rules" or anything like that. It's more of a "hey this is my wife LR, this is So and So," then, generally, I would go on my way to whatever activity I have planned unless the other person had specifically requested we all do lunch or coffee or whatever.
The REASON we do it that way, is that it tends to reduce the chances that the new person gets it in their head that they are getting a single man, when they aren't.
Likewise, I don't consider ANYONE a potential lover if they haven't met my husband AND my boyfriend (who lives with us). Not a chance. I always (no rule here, just my personal preference) meet new people WITH one or the other (hubby/bf) and then go from there.
Same reason, I want them to KNOW I am in happy relationships. My availability has nothing to do with the TYPICAL mono-assumption that I am in an unsatisfying relationship and "on the prowl for someone new" so I can leave.
It really helps ensure that the POLY is kept in our poly arrangement.
It's much easier to build up to a healthy romantic relationship with someone who is fully accepting of my dynamic (and I KNOW IT because they've met and been around my lovers comfortably) than it is to establish a HEALTHY romantic relationship with someone who has no contact with my lovers.
So-to sum it up-you can do it anyway you want to.
But, those of us who want to meet asap-have some valid, healthy reasons for it.
As much as I'd love to say there was no longer any issue of cowgirls/cowboys being on the prowl for polys-it would be a lie and these people can reek way way more drama in a relationship than is worth dealing with.
"Love As Thou Wilt"