Hi,
YES, co-op/internship/work experience term, which are mandatory part of a course will be counted for PGWP.
If you do a 8 months course(2 SEM) with 2 months co-op or full 1 SEM co-op then subsequently you 'll get a 8 months+2 months= 10 months PGWP or 8 months+ 1 SEM(4 months)= 12 months PGWP.
So, course duration+no. of months mandatory co-op = total duration of post graduate work permit.