Canadian Time Zones
Currently the switchover to DST occurs on the 2nd Sunday in March, and the return to the standard time occurs on the 1st Sunday of November.
Current time zones
From WorldWeb Travel Guide:
Canadian Standard (Winter) Time, October 26, 2003- April 3, 2004
Daylight (Summer) Time: see below

Pacific

Mountain

Central

Eastern

Atlantic

Nfld


2004 ST

Canada has six time zones:
Newfoundland Standard Time (NST) 3 hours from Greenwich
Atlantic Standard Time (AST) 4 hours from Greenwich meridian
Eastern Standard Time (EST) 5 hours from Greenwich meridian
Central Standard Time (CST) 6 hours from Greenwich meridian
Mountain Standard Time (MST) 7 hours from Greenwich meridian
Pacific Standard Time (PST) 8 hours from Greenwich meridian

Some provinces use Daylight Saving Time: In 2004 the clocks were turned forward by one hour on the first Sunday of April and turned back on the last Sunday of October. Since only some parts of the country practice Daylight Saving Time, time zones look very different in summer.

Many people wonder why Newfoundland has a time zone that is a half hour different rather than one hour. The system of Standard Time employs 24 meridians and each are theoretically the centres of 24 Standard Time zones. Newfoundland lies squarely in the eastern half of its time zone. Newfoundland is not the only place in the world where half hour time differences are seen. Suriname, Iran, India, Sri Lanka, and Central Australia also operate on this difference.

Canadian Daylight (Summer) Time, April 4, 2004- October 31, 2004

Pacific

Mountain

Central

Eastern

Atlantic

Nfld


2004 DST

Newfoundland Daylight Time (NDT) 2 hours from Greenwich
Atlantic Daylight Time (ADT) 3 hours from Greenwich meridian
Eastern Daylight Time (EDT) 4 hours from Greenwich meridian
Central Daylight Time (CDT) 5 hours from Greenwich meridian
Mountain Daylight Time (MDT) 6 hours from Greenwich meridian
Pacific Daylight Time (PDT) 7 hours from Greenwich meridian