Graduate School Offer of Acceptance Due Dates in the US? I am applying to biomedical science Ph.D. programs, and the programs have very different deadlines for applying. For instance, many applications were due at the end of Nov/start of Dec, however, I have several due mid-Dec to mid-Jan. 

Already, I have received an offer to follow up with an interview at the University of Arizona for their Ph.D. program, even though I have not submitted my final 2 applications due over the next month.

Does anyone know if Ph.D. programs tend to be strict about when one can accept an admission offer from a Ph.D. program (i.e. giving an applicant 1 week to accept an offer or decline it)? My worry is that if the University of Arizona offers me admission, I will only have a few weeks max to respond (likely before I even interview for other programs, if I am to be chosen for interviews). I know when I applied as an undergraduate, I was given a lot of time to choose my school. However, when I applied to summer internships throughout college (e.g. Amgen Scholar), I was given 5-7 days to respond with my decision on whether I want to partake in the program that offered me admission.
As noted by @NateEldredge in a comment, almost (and I only say "almost" because even one exception would preclude saying "all") every university in the US admitting students to a biomedical sciences PhD program does so based on the April 15 resolution:


  Students are under no obligation to respond to offers of financial support prior to April 15; earlier deadlines for acceptance of such offers violate the intent of this Resolution. In those instances in which a student accepts an offer before April 15 and subsequently desires to withdraw that acceptance, the student may submit in writing a resignation of the appointment at any time through April 15. However, an acceptance given or left in force after April 15 commits the student not to accept another offer without first obtaining a written release from the institution to which a commitment has been made. Similarly, an offer by an institution after April 15 is conditional on presentation by the student of the written release from any previously accepted offer. It is further agreed by the institutions and organizations subscribing to the above Resolution that a copy of this Resolution or a link to the URL should accompany every scholarship, fellowship, traineeship, and assistantship offer.


This means that you will not have to accept any offer prior to April 15th, and that no accepted offer is binding until after April 15th (though it would still be impolite to accept and then withdraw, so this should only be done in extreme circumstances). The explicit purpose of this resolution is to not allow universities to pressure students to accept an offer before other schools are done presenting their own offers.

Once you know for sure which offer you want to accept (and no earlier), however, it's good to accept as soon as possible and let other institutions know you will not be attending - this can let them extend offers to people on their waitlist and therefore gives those waitlisted applicants more choice.