this link- https://www.publicsafety.gc.ca/cnt/ntnl-scrt/crtcl-nfrstrctr/esf-sfe-en.aspx i found within below link only-The confusion here is the other link you posted from IRCC twitter which clearly states the temporary full time waiver applies for an essential occupation whilst classes are in session. yet you have an answer above from IRCC which appears to contradict this versus this link
https://www.canada.ca/en/immigration-refugees-citizenship/news/2020/04/removing-barriers-for-international-students-working-in-essential-services-to-fight-covid-19.html
Ultimately your decision given we all here can only go with interpretation as per the guidelines
https://www.canada.ca/en/immigration-refugees-citizenship/news/2020/04/removing-barriers-for-international-students-working-in-essential-services-to-fight-covid-19.html.
See below - "Guidance on Essential Services and Functions in Canada During the COVID-19 Outbreak"
"International students and their employers should consult Public Safety and Emergency Preparedness Canada’s Guidance on Essential Services and Functions in Canada During the COVID-19 Outbreak to determine if the work the student is doing would allow them to work more than 20 hours per week during the academic session."