It won't be "a few minutes vs today." The bus stops and you get off, walk to the escalator and ride it down to the platform.  You wait for the train. You and a hundred other people crush aboard. Yes, there will be a crowd because UW station is convenient for so many. Just a "few minutes?" Unlikely. Convenient? No way today.  The UW switch only becomes better when Sound Transit forces buses off city streets.   
But hey, 520 riders, consider yourself lucky.  On April 7, 2017, Sound Transit announced, "Sound Transit and Metro routes that currently travel from east of Mercer Island to Seattle via I- 90 would be rerouted to other Eastside communities, deleted, or modified to begin and end at Mercer Island where riders could transfer to the regional light rail system. Westbound buses would not continue into Seattle under the proposed Transit Integration refinements."