"E" is Eastern Time Zone, "C" is Central Time Zone, "M" is Mountain Time Zone, and "P" is Pacific Time Zone. Occasionally, an area code will fall in more than one time zone. In this case, the abbreviation is a combination of the previous abbreviations. Some area codes are shown with time zones referencing Universal Coordinated Time (UTC).
Additional technical status can be retrived from the North American Numbering Plan Administration on the 778 area code specific link here.
Area code 778 went live into service on November 03, 2001 (The paperwork process started on August 17, 2000).  It was formed as a subdivision of the 604 area code.
This area code went live on November 03, 2001 as an "overlay" on the 250 area code. This means the 778 area code was created in part to provide more telephone numbers for people in the 250 area code area. In other words, 778 is a subdivision of the 250 area code.