On modern calendars they mark the Passover on the correct day. However, Jewish days are from sunset to sunset. So this year, the Passover started Friday evening and lasted all day Saturday until sunset. That's why the Passover is marked as Saturday (this year) because the majority of the hours occur on that day. It's confising, but just think of sunset as the equivalent of our midnight. So no matter how idiotic JWs are, so long as they observed the occasion this year after sunset on Friday, they observed it on the correct date.
No matter what the time zone, the date is the date.
Theres plenty of other bullsh!t teachings to criticize them on. Let's at least use one that has some legs to stand on other than the timing of the memorial.