One year of study means 2 semesters, which are 4 months each, 8 months in total.
2-year study programs are 4 semesters or 16 months.
2-year programs normally take summer breaks, so you end up studying for 16 months and having two 4-month breaks in between. But some are called "fast-track" programs that don't have summer breaks, so they take 16 months to complete (4 consecutive semesters).
For 1-year programs, you get 1 year of PGWP
For 2-year programs, you get 2-3 years PGWP (as stated by IRCC, but I've heard almost everyone gets three years).
For 3-year programs, you get 3 years of PGWP.
Not sure about 4-year programs.