Station stops typically add about 2 to 3 minutes to GO schedules, depending on the speed limit. Breslau is in a 70 mph zone so I'd guess slightly over two minutes.
The Kitchener Expansion BCA describes a 90 minute travel time for express trains including extra stops at Breslau, Malton and Woodbine (Pearson Junction). Today the travel time is 101 minutes, though I expect that to drop to around 98 minutes in the next timetable.
A more optimistic theory is that GO is assembling properties on the south side of the tracks to make room for another pair of tracks. And the surface parking lots are just a placeholder until that happens.