The NCAA doesn’t recognize P5 and G5. That’s created by external forces, largely bowl contracts and sports media.
Only FCS and FBS are recognized by the NCAA, and Northern Illinois is FBS just like the Utes. Idaho State is FCS, and there is a rule that only one FCS team a year can count towards bowl eligibility, essenitally ensuring an FBS school doesn’t schedule more than one FCS game a year. It actually used to be, you could only count an FCS team (D1-AA at the time) every other year, so the current rule is more leniant in that regard.
I don’t think you need to worry about a full stadium. 11:00 AM will put a damper on tailgating, because that’s pretty earlier for the pre-game festivities, but fans want to see this team play in person.