Ok I was in a similar PGWP situation a couple of years ago: when people first apply for study permit, they normally are granted with however long the study period is plus three to four months for applying PGWP, but for me, because of my co-op, I graduated four months later than the normal study period, which is right before my study permit expired. I consulted with the international student office at my school, and was informed that I can just apply for PGWP and can legally work during the waiting period, and can show my employer the confirmation that CIC received my application (back then I didn't know this is implied status). I also confirmed with my employer (which is my school actually) about the work permit situation since I started working part-time one month before graduation and the HR confirmed the same thing. But, as paranoid as I am, I actually applied a study permit extension for four months and put the reason as "potential gap between study permit and PGWP", and maybe an off-campus work permit (I couldn't remember actually, it was around the time they changed the rules) so I know I was covered by legal status. But when I apply PR under CEC, I didn't count the time during this period since I wanted to be 100% sure regarding the qualifying period. Hope this helps.