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... but when does April 1 really start? To discount the effect of time zones, it's best to go by a common time zone (like how TV shows are always listed in EST/EDT in the US even though they're also seen in other time zones at other times). For a website with an international audience, the only time zone that makes sense is GMT... and it's already been a couple of hours into April 1 GMT.
(Do we really have to remind people about this every year? Sigh.)