Dear friend is still waiting to hear from alumni about a possible interview. Doesn’t all the feedback need to be in by Feb 28 for a March 31 decision roll out? When is the latest someone might be contacted by an alumnus for an interview?
If the student hasn’t already been contacted by now, it’s doubtful one will be offered. For my Ivy, our reports are due on 15-Feb. But all the names were assigned by mid January, at latest. Interviewers are generally instructed to initiate contact right away, even if the actual mtg takes place later. Since there’s been no contact already, I doubt a call will come. I don’t know the numbers for PTon, but for my college, only 5% of alums do any interviews. The applicants greatly outnumber the available interview slots.
There is still time. Princeton alumni interview over 99% of the applicants, and they usually conduct them through all of February.
I have a friend whose is next week. Don’t Worry! There’s still time 
My son will have an interview on 2/22. So it is still happening.
I was also just contacted two days ago.
My daughter just had her interview today and it was great!
DS just had his today and it went well!
I thought I wouldn’t get an interview, but I just got contacted today for one. (Unscheduled as of now.) Judging by other comments on this thread, I’m guessing that Princeton’s deadline for interviews to be all conducted extends longer than other schools.
I had mine on Friday, so yeah, Princeton is probably the Ivy that conducts them the latest.
I literally just got a call about one today, and will be doing my interview on March 1st. So yeah, there’s time.
My son had an interview in January and it was a good experience. That said, I’m fairly dubious about the value of an interview. I view them as a way that the college/university makes their alumni feel valued and connected to the school but as having little if any substantive impact on an admissions decision. If something were grossly wrong–if a candidate appeared dangerously unbalanced or threatening I would guess that that would be noted. But for the most part I think they’re courtesies, especially at highly competitive schools.
I completely agree with everything @zzzmmm said ^.
Just had mine today. I think these go out pretty late