In (most of) the United States, daylight saving time [DST] begins on the first Sunday of April (clocks are set forward one hour; so 3 pm becomes 4 pm) and ends on the last Sunday of October (clocks are set back one hour, so 5 pm becomes 4 pm). With some convolutions with the Weekday function, you can find out when these will fall in any year.
G'luck.