How did they know where they would arrive..?

[Brainslinger]

I believe the ambush was a combination of the various villains working in conjunction.

We know that the mobsters were putting pressure on Calvin Tower to sell the Lot. Due to Toren's carelessness, they were easily able to track Tower to the correct town, although they were unaware of the address. The spying Mia likely heard the plan concerning the ka-tet picking up Toren's forwarding address from the gas station and probably sent the information to Sayre, who in turn sent the mobsters to stake out the station. They probably didn't know that Roland and Eddie were the ones that were coming through, but they knew someone would and were gunning for whoever turned up. The gangsters weren't necessarily aware that the guys would turn up out of thin air, or that other worlds were involved at all, just that they had to wait at the gas station.

How they knew the date and time, I'm not sure. Likely Sayre would have had an idea of how much time passed in the keystone world in relation to End-world to make an estimate. Either that or Walter or the Red King 'precogged' the info.

Of course considering Mia and Sayre's plan to take Black 13 with them, the door back to the keystone world should have been permanently closed from Sayre's point of view (I'm sure he's the mastermind in this case although Walter might have taken a role too) but it makes sense that they'd take care of every eventuality. Especially as Sayre was probably unaware exactly when they would cross over from End-World. For all he knew they'd do it before Mia had escaped (remember they were planning on coming to the 70s before Mia altered their plans somewhat.)

[Wuducynn]

How they knew the date and time, I'm not sure. Likely Sayre would have had an idea of how much time passed in the keystone world in relation to End-world to make an estimate. Either that or Walter or the Red King 'precogged' the info.

Of course considering Mia and Sayre's plan to take Black 13 with them, the door back to the keystone world should have been permanently closed from Sayre's point of view (I'm sure he's the mastermind in this case although Walter might have taken a role too) but it makes sense that they'd take care of every eventuality. Especially as Sayre was probably unaware exactly when they would cross over from End-World. For all he knew they'd do it before Mia had escaped (remember they were planning on coming to the 70s before Mia altered their plans somewhat.)

This is some interesting ideas here, Sayre working in conjunction with information from Walter or even from Los' himself. Makes a lot of sense the more I think about it.