Bedrockgames
I post in the voice of Christopher Walken
No, your choice doesn't really matter here. What matters is that in this scenario there is only 50% chance to meet Bill in given location, but this would be exact same situation if there was Quantum Bill with 50% probability and the GM would just flip the coin once the PCs arrive in one location to see whether Bill is there.
Even if it is a 50/50 shot, if the GM decides where Biff is first, then it is a meaningful choice because one way leads to Biff immediately, the other doesn't. If I meet Biff no matter which way I go, not only do I not have a meaningful choice, but it is now a 100 percent chance of bumping into Biff. That is a huge difference on both counts. Also how informed this choice is will be very dependent on how players make their decision and how the GM decides which way to go. But assuming they have zero info, and Biff is just randomly at one of the locations, as a player, I'd still like to think, even if it is just a shell game, it is an honest shell game, not the GM saying "its the same either way" and insisting the encounter happens down both paths.