I've purchased a bus ticket from Amtrak to go from Vancouver to Seattle and the booking page displayed a warning about special conditions for passengers crossing the border:
Passengers traveling from Vancouver, BC, to the United States should arrive at least one hour prior to departure for border crossing processing.
However I presume that this warning only applies to trains, as buses only go through border control at the actual border, rather than at the train station. But the Amtrak page fails to mention the check-in times for their bus anywhere on their website and likewise my ticket doesn't. Where can I locate this information?