So what is the time Frame to be considered or not considered a blue blood? 25 year span, 50 years span, 100 year span? I would say that 75-100 year range. Basically if there is nobody left alive that remember when you were good, you are no longer a Blue Blood.
To be considered a Blue Blood it gets a bit more hazy. I would say you can't be considered a blue blood unless your program as been D 1 for at least 50 years.
I'd agree with you on the time frame of 75-100 years.
I also agree that Blue Blood is at best a nebulous term, but in my mind indicates long term and consistent excellence on the gridiron.
The Florida schools do not meet that criteria despite their recent(?) 30-40 year history of being very good.
Army dominated the first half of the previous century, had they been as good since, then I would consider them a Blue Blood.
Though it would be unpopular I would almost put Harvard and Yale on that list simply because they play as excellent football today as they have for 150 years and that at the very least deserves consideration.
Go Blue!