If you really want to separate the "Keep Bronco" vs the "Move On", instead of asking when they started being a fan, I believe the question to determine separation is simpler:

"Before this season began, how did you expect this team to perform. Not in your 'I'm being a rational fan' pessimism, but really and truly inside, what did you expect?"

Keeper - "8 wins expected, 7 disappointing, 9 would be a pleasant surprise - Beat the bottom third of the schedule, (FSU, SJSU, Wagner,Uconn) Then let's go 3/4 with the middle third - who are no slouches (USU, BSU, ECU, Cinci) then lets steal one from a team that we are obviously athletically inferior to and will likely be considered underdogs to. (Neb, UCLA, Mich, Mizzou). 8 is reasonable, 9 wins would mean that we either swept the middle third and still stole one from the premier teams, or that we had a respectable 75% in the middle third and stole TWO from the elite teams.

Move On - "Even though 6 of the teams we face will have higher recruiting classes than we do (i.e. more talent), I would be upset if we don't win at least 10 games. Everyone who makes millions and millions of dollars analyzing these games and athletes is wrong. We are at least as talented as Mizzou, UCLA, Mich, and Neb. so should at worst go 50/50 there. Even though the professionals in sports broadcasting and Vegas will likely pick us at 0-4 in those games, if we aren't at least 2-2, someone should be fired. As for BSU, USU, Cinci, ECU. They don't even have athletes there - we should win every one of those handily. And let's just send out the Freshman team for the bottom 4. Why even play those? 10-2 or bust!!

I think you can probably tell where I sit, but in all honesty, I was a fan since the 80's. In the 80's BYU was favored in almost every game they played. They won almost every game they played, but they still lost a lot they were expected to win. I would say that parity has hit hard in CFB. BYU is not favored in 10 or 11 games a year anymore. That's a product of the harder schedules, Independence, and most of all P5 inclusion and recruiting. None of those are Bronco's fault. I believe he does admirably with the athletes and schedule that he has.

I don't follow vegas that closely, but this year, correct me if I'm wrong, but Bronco to this point has won every game he was favored to win, and at least one (I think two) that he was expected to lose. Not a lot of coaches who lost (arguably) the two best players on their team can say that.