It's MRI's biannual PSA reminder about that daylight savings time clock thing that has been going on, and off in the US since 1918. DST has not been always very consistently applied in the US due to state, and federal legislators mucking around with the issue. In the early sixties a 35 mile ride on Route 2 between Moundsvile WV, and Stuebenville OH required 7 time changes. In 1966 the Uniform Time Act was enacted, and Daylight Savings Time became generally standard, but states could still opt out of the program, but at least the entire state would have to opt out, sort of. Arizona, with the exception of the Navajo reservation, and Hawaii do not use DST. Why? I don't have a clue, maybe they they just have a lot of extra photons to waste.
So in sum, the GMT offset for Eastern Standard time is now -4,00 hours. so check, and if needed change your chartplotter's offset from the -5.00 hours on Saturday to -4.00 hours on Sunday if you're in the eastern time zone. Add one hour for each time zone going west. If your chartplotter's clock is off, it shifts the tide calculations, and in some cases the estimated time of arrival. Ahem, for those of you who may be clock challenged, this means you move the little clock hand forward one hour. Leave the big hand alone. Or is it you move the big hand all the way around once, and the little hand will follow. Heck, I'm not sure, my VCR has been blinking at me for two decades.