Upvote:2
In short, each day in the Schengen zone you are allowed to have been there 90 days in the last 180 days, including the day you are. It is a rolling system, not sharp edged periods of time.
So when you return from Eastern Europe your first days in the Schengen zone will have rolled out of the 180 days window, but the 80 days starting in June will not. Or at least not all of them.
Upvote:2
Consider this thought experiment. Of course it is not practical to actually do this every morning, but I'm trying to explain the principle.
There are some exceptions to this which allow longer stays, notably for holders of a D long-stay visa, and also "grandfathered" bilateral treaties between Canada and individual Schengen nations. For instance, you can spend days beyond 90 in Denmark, but days in Denmark early in the trip do count against those 90 days as far as other Schengen countries are concerned.