As soon as you submit your PGWP you can start working full-time (there are some conditions).
Students who have completed their program of study
Students who have completed their program of study are allowed to work (under paragraph 186(w) of the Immigration and Refugee Protection Regulations [IRPR]) while they are waiting for a decision on their post-graduation work permit application, provided they meet all of the following criteria:
they are or were holders of a valid study permit at the time of the post-graduation work permit application
they were a full-time student enrolled at a DLI in a post-secondary academic, vocational or professional training program
they were authorized to work off-campus without a work permit