Little more information on the games:
2019: Game at Tennessee will be September 7
2023: Game at BYU would be either September 1 (Friday) or 2 (Saturday). If someone made me bet right now I'd guess Friday because if BYU stays independent then ESPN will be the television and they like the BYU Friday night thing.
Mind you that it was not a foregone conclusion that the game would be in September. As an independent, BYU has to schedule home games for November and, occassionally, can entice a Power 5 team like Georgia Tech to come in November. For a team like Tennessee that could be disastrous as the temperature tends to drop into the 30s and 40s then. As it is, with the low humidity a September 1/2 game would be probably the best weather you can imagine. Start time temp around 75 and a slight chill in the air.
Looks like Tennessee was the initiator if I'm reading BYU's AD's statement right: "There's something about those orange and white checkerboard end zones that shouts 'Tradition!'," BYU director of athletics Tom Holmoe said in a university release. "When the opportunity to play a series with Tennessee presented itself, we didn't blink. They're a storied football program with a winning tradition, national championships, a classic stadium, incredible fans and hall of fame coaches. It will be a great experience to visit SEC country and play in Neyland Stadium, and later host Tennessee in Provo."