Swearing in ceremony dates for newly elected terms of office, and yes, they do vary

For the details check the Secretary of the Commonwealth's page ->
https://www.sec.state.ma.us/ele/eledatesofoffice/datesofofficeidx.htm?s=03

MA General Law also outlines the oath of office

https://malegislature.gov/Laws/GeneralLaws/PartI/TitleXVIII/Chapter125/Section10

for Town Clerks - >   https://malegislature.gov/Laws/GeneralLaws/PartI/TitleVII/Chapter41/Section107

(If someone has a better source, please let me know and we'll update this)

For the details check the Secretary of the Commonwealth's page ->