Every countdown is worked out against your site's own time zone — the one under Settings → General — and sent to the browser as one exact moment rather than a time of day. A visitor whose device clock is slow is corrected against your server's clock, as far as the page can tell: fully on a page straight from your site, and on a copy from a page cache only as far as the moment that copy was made. One that runs fast counts by its own clock, because on a cached page a fast clock and an old copy of the page look the same.

The dashboard shows which zone your site is on, and the campaign editor says it next to the date field, because a countdown that is an hour out is the one mistake this plugin cannot make quietly.

An end is kept as your site's own date and time, so changing the zone under Settings → General moves the moment every fixed-date campaign ends. The plugin books the moments sales open or close again at their new time, and, while Enable countdown timers is on under Settings and a campaign is switched on, empties the page caches it knows once the change is saved, because every cached timer carries the end worked out in the old zone. An end the new zone puts in the past takes effect at once: an offer closes, a launch opens.

The clock, and the time zone