It says it doesn't work on iOS Safari, but iOS users can get the "Clock Wave" app from the app store which does the same thing. (And allows fun time zone tricks with clocks from other countries.)

thank you for this reply! i've got 6x CASIO watches and have struggled to the time on them synced for over a decade. a quick [small] purchase later and every single one of my CASIOs are synced. i'm so happy. its the little things that matter. thanks again.