Ah, yes...(ahem, in my most academic voice) "Ya'll", or sometimes spelled "y'all" or even "yall" is ubiquitous to the Texan dialect, although it has variations throughout the South. It can be singular (as in, "Hey, Bubba, ar ya'll goin' diving this weekend?") or plural, (as in, "Hey, do any of ya'll know any good divin' sites?"). Many times, the term is possessive, though that form requires creative spelling. ("Is this dive flag ya'll's? I woulda sworn I left mine here somewheres.")
As for the proper waiting period, that's a matter of proficiency. Upon arrival and for at least some time afterward, a newcomer needs to pay close attention to the pronunciation, emphasis, and timing in the way locals use the word. It is important to note that the word is a single sylable. A cardinal sin is to mispronounce it as "you-all", or (possibly worse) "youse-alls". Natives have been known to get testy with such (mis)usage. However, with care to detail and proper decorum, you (or better yet, YA'LL) should be able to use the term properly very quickly after getting settled in. In fact, you will probably find that when you return to New Jersey, say for Christmas, your family and friends will many times wrinkle their noses or perhaps break out in giggles as they ask, "What happened to you? You're talking so funny and you have a...a...ACCENT!"
It will tend to rub off on ya'll with time.