Catholic saint feast days, Constitution Day, and implementation flexibility via regulation

As a service to Catholic school administrators everywhere, I thought I would link to a listing of Catholic saints whose feasts fall on September 17 (at least according to the Internet). It turns out that the feasts of St. Hildegard of Bingen, St. Robert Bellarmine, St. Lambert of Maastricht, St. Satyrus of Milan, and St. Ariadne of Phrygia, among others, are celebrated on September 17. That is also the day that Congress has statutorily designated as Constitution Day. 

By seeming statutory mandate, every educational institution that receives federal funds "shall hold an educational program on the Constitution" on Constitution Day. See Section 111 of Division J of Pub. L. 108-447, the "Consolidated Appropriations Act, 2005," Dec. 8, 2004; 118 Stat. 2809, 3344-45). This requirement is inflexible as to date. The required educational program must be held "on September 17." As it turns out, though, the Department of Education has provided greater flexibility in certain circumstances. In federal regulations issued in May 2005, 70 Fed. Reg. 29727, the Department of Education authorized a two-week window for the required program, but only when September 17 falls on a Saturday, Sunday, or holiday:

Section 111 requires that Constitution Day be held on September 17 of each year, commemorating the September 17, 1787 signing of the Constitution. However, when September 17 falls on a Saturday, Sunday, or holiday, Constitution Day shall be held during the preceding or following week. 70 Fed. Reg. 29727.

Hence this post's opening identification of Catholic feast days on September 17 (which this year is a Wednesday). The regulations do not define "holiday," but a Catholic educational institution receiving federal funds might be able to obtain some flexibility in the timeline for compliance with the Constitution Day requirement by explaining that the feast of St. Robert Bellarmine or St. Hildegard of Bingen, say, is a "holiday" within the meaning of the regulations. 

There are a couple of reasons for caution, though. First, this is a bit of a stretch regarding "holiday." But then again, the proviso authorizing an alternative date for compliance seems entirely made up anyway. Second, and relatedly, the regulations may be invalid because they conflict with the statutory requirement. I've asked around casually but have not been able to find good answers: What is the best argument that the Department of Education acted within its statutory authority when authorizing a different date than September 17 for holding an educational program to comply with the statutory requirement? Is there some kind of administrative law analogue to Fed. R. Civ. P. 6(a)(1)?

Having run the analysis thus far, I may as well finish up by noting a split of interpretation on whether there are any practical consequences under the law for failure to comply with the educational programming requirement. Some have suggested that non-compliant institutions may place their entire amount of federal funding at risk (which would probably be unconstitutional under NFIB v. Sebelius), while others have suggested that the requirement is entirely precatory. I tend to agree with the latter understanding. 

(Bonus question: What prominent ongoing cases does the foregoing bring to mind with its discussion of regulatory implementation flexibility contrary to statutory text and its consideration of whether "shall" is precatory?)