DST is a practice of adjusting the clock forward one hour during warmer months to make better use of daylight. In the United States, DST usually starts on the second Sunday in March and ends on the first Sunday in November. In Switzerland, DST also begins on the last Sunday in March but ends on the last Sunday in October.
When both NYC and Zurich are observing DST, the time difference is five hours. For example, if it is 12:00 PM in NYC, it will be 5:00 PM in Zurich.
When DST is not being observed in either location, the time difference is six hours. For example, if it is 12:00 PM in NYC during standard time, it will be 6:00 PM in Zurich.