Around what time during the year do we find out the day exams are scheduled?

Sometime in november, so not for a while.

The tentative exam schedule is usually released towards the end of November. Your profs will often discuss in class your exam date when the schedule is released.

Originally Posted by Leppinae

The tentative exam schedule is usually released towards the end of November. Your profs will often discuss in class your exam date when the schedule is released.

The tentative one is earlier, usually end of October. By the end of November, with exams right around the corner, the final one should definitely be out.
As the term progresses, the approx date of the final timetable will be released here: http://registrar.mcmaster.ca /scheduling/examtt.html
(This is also the location of the final timetable).

And if you're booking vacations, you should wait until the final schedule is released. If you go off the tentative schedule, the Registrar's Office and your Associate Dean's office will not be willing to help you (and cannot) reschedule.