Just a heads up, we're expecting 6-10 inches of snow, but perhaps a lot more on Wes night and Thursday this week. I'd still lay money on Princeton informing this week but Snowmagddon is really disruptive. And it could really stop now. Please.
If Princeton hasn't dropped today, than I'd say either tomorrow or Thursday/Friday next week. I have no insider knowledge about this cycle other than the culture of the department. There is some variability because these things will be sent out by the graduate assistant who is new to the department.
You haven't necessarily been waitlisted. At my (exceedingly middle-of-the-road) program, we divide the applicant pool into tranches. Last year, out of about 100 applicants, there were 70 or so who were not getting in under any circumstances--we do not admit PhD students without funding. Those letters go out immediately. Of the remainder, we select our top eight--for six funded slots--and usually make offers to those pretty quickly. Becuae we are not a top program (see above), many of those students will have accepted better offers elsewhere. A few will keep us hanging, using our offer to get a little additional consideration from their top choice (and more power to them!) We don't begin to move down the food chain to our second tier of candidates until we have heard a definitive "no" from the top choices. That can take four to six weeks--and our committee meets later than any other I'm aware of. We don't give anyone we might otherwise conceivably take a firm "no" until it's clear that we won't be making an offer because our class is made.
An unsolicited piece of advice, and one that I would have been constitutionally unable to take when I was in the throes of the admissions process: Don't let this be a hellish weekend. Try not to log on and check the results page every twenty minutes. If you're going to make this a career, acceptance to a PhD program is just the first, and the most low-stakes, version of a hundred weekends you'll spend. If you let it define your life, there will be agonzing time waiting for responses from comps, fellowships, grants, referees' reports, dissertation committees, hiring committees, editors' reports, promotion and tenure committees, book reviewers... it will make you insane if you allow it to. If you have done the best you can do with your application, try and let it go... the results will work themselves out. Read something. Pick up a hobby, preferably one that involves saving money.
This is easier advice to give than to take--I'm in the middle of a decent career here, and it is still hard to turn off the anxiety switch some days. But you will be much happier, and much more productive, if you can develop a sense of detachment on things that are out of your hands. You will be fine even if you don't get in to a doctoral program. Trust me on that.