As the United States starts DST on the second Sunday in March and ends it on the first Sunday in November, Mexico's time zones are out of synchronization with American and Canadian time zones for two periods each year. The first is the three or four weeks between the second Sunday in March and the first Sunday in April. The second is the single week between the last Sunday in October and the first Sunday in November. During these periods, clocks in Mexico City match those in Denver rather than those in Chicago. The Mexican Stock Exchange changes its hours during these periods in order to maintain synchronization with the U.S. markets. Conversely, television schedules are not changed for these situations, meaning Mexican television networks which are carried directly by American cable and satellite services have their programming aired an hour behind in the United States during these interregnums.