Last time the Cougars were on ESPN, in prime time, at LES it was a disaster (Utah).

Network	Week	Visitor	Home    Result
ESPN2	Week 3	Utah	BYU	L; 54-10
ESPN	Week 4	UCF     BYU	W; 24-17
ESPN	Week 5	Utah St	BYU	W; 27-24
ESPN2	Week 11	Idaho	BYU 	W; 42-7

As the Utah game was on ESPN2 I pulled the home games that were on ESPN2 or better. And each of them would likely fall near what you considered to be primetime of 9PM EST (Utah = 9:15PM ET; UCF = 8PM ET; USU = 8PM ET; Idaho = 9:15PM ET).

Note if we were just listing ESPN in general (all of their channels) we also had home games with SJSU 10:15PM ET and NM St 10:15PM ET that we won since the Utah game.