Every proof ever seems to have used it, I don't think Q officially said it. But it makes sense because 1) Trump/Q are based in the White House in Eastern Time zone, but far more importantly 2) if we could use any timezone, it would be completely meaningless as there's 24 time zones to cherry pick any hour you want, thus we'd have to ignore the hours and only focus on the 0-60 minute part of the clock which limits it. Q always uses ET which is DC local time with daylight savings. I can show proofs if you want that switch between EST and EDT showing they always use ET.