Atlantic Daylight Time (ADT) is a time zone that is four hours behind Coordinated Universal Time (UTC-4). It is observed in parts of eastern Canada, including Nova Scotia, New Brunswick, and Prince Edward Island, as well as some Caribbean islands. ADT is used during the summer months when clocks are set forward by one hour to make better use of daylight. When standard time resumes in the fall, these regions switch back to Atlantic Standard Time (AST), which is UTC-5. The transition to ADT typically occurs on the second Sunday in March and reverts on the first Sunday in November.