For me, relationships are things that just grow and happen so I can see where they may be coming from. That doesn't mean that it isn't a process - it is just a process that happens at it's own pace. So, you keep talking, and visiting, as friends, and if something at some point develops then...good!
Which isn't to say that you don't make plans - it's that you don't make plans that have an expected outcome. You make plans to keep lines of communication open with people you find interesting (as friends, not just "potential partners"), to keep yourself STD free, to meet people and socialize and keep yourself open to possibilities should they arise.
So, with regards to STD testing for instance, maybe it is reasonable to get STD tested once a year, or every six months, or every time you have an potential exposure. You make a personal rule for yourself about use of protection. You share this as a "good idea" with your friends (ALL of your friends - it's pretty much a good idea anyway). The point is, then you are prepared on your side, to have the STD talk with any potential new partner - not just them.
You invite them out to visit as friends without the expectation that something more necessarily develop on this trip. You come out to Pittsburgh to see them and maybe other friends that you have in Western PA. Come for a concert, plan to go to a poly Meet-Up with them, etc. Maybe something develops with one or both of them, maybe you meet someone entirely new...
Things can develop in a "right and good way" without following a pre-set script if you keep your eyes open for things as they develop and set for yourself a policy of honesty and integrity with all people at all times. I don't know that there is a time-frame for waiting - more of a "personal readiness" on the part of each person.
Be patient, be prepared, be open, be yourself. Enjoy the people in your life now, enjoy the relationship you have with each person (and yourself) for what it is now (not what it could become), enjoy the moment and the place you are at. And when the next moment comes? Savor that one as well.
Me: poly bi female, in an "open-but-not-looking" Vee-plus with -
MrS: hetero male, live-in husband (together 21 years, married 17)
Dude: hetero poly male, live-in boyfriend (together 2.5 years) and MrS's best friend (for several years longer than that)
Lotus: poly bi female, dating Dude; married to TT, poly male
VV and MsJ: bi-women with male primaries, LTR LDR FWBs to JaneQ
My poly blogs on this site:
The Journey of JaneQSmythe
The Notebook of JaneQSmythe