There's a 1 in 365 chance the first time-travelers, aliens or some other cool event will happen on April 1st, so it's your loss if you miss it! :P
Because I'd posit that the vast majority of the human world we experience today was shaped by chance events that nobody noticed.
Further more, I'll mention there is some crazy Russian who thinks our modern calendars (Gregorian) are an elaborate hoax. But, as I understand it, he had someway of applying algorithms to historically "significant" data points. (If you're actually interested, reply and I try and find his name again.)
...FWIW
I also think it's rather unlikely that true time-travelers would use April 1st, unless they were trying to be funny. And if I discovered cold fusion and it was April 1st, I'd take an extra day to iron the bugs out :-P