What is server time? Why a website's clock differs from your phone

Written 2026-11-01 · Updated 2026-11-01

The sale opens on the website's clock

When a sale "opens at 10:00:00", it opens when the computer running that website says it's 10:00:00. Your phone has nothing to do with it. If the site's clock is still at 9:59:59 when your phone shows 10:00, your click arrives before the sale has started.

Phones set their clocks automatically from the network and are usually right to within a fraction of a second. Servers are normally synced to standard time too, but how well depends on how each one is run.

How far off can it be?

Some of what we have measured:

• Three large ticket sites in Korea were within a few milliseconds of standard time.
• One university's registration server ran about 1 second slow. Clicking at exactly 10:00 by your phone meant clicking a second early by that server.
• Another university's server drifted about 2 seconds a day, and once jumped 0.676 s in a single step when its clock was reset.
• One ticket resale site runs several servers whose clocks disagreed with each other by up to 0.7 s.
• More than ten ticket and shopping sites in the US, Europe and Japan matched standard time within their measurement margins.

So a site that was right yesterday can be off today, and a big, well-run site is usually close. You only know by measuring close to the opening.

How we measure it

Every web server sends the current time with each response (the Date header), but only to the whole second. One request tells you "around 10:00:03" and nothing finer. To find the exact moment the server's second ticks over, we send requests timed to arrive right at that moment and halve the range with each answer, down to a few milliseconds. Every reading shows its margin (±ms) next to it, and we don't use a reading whose answers were too few or too scattered.

What we can't see

Large international sites answer from a network of front-end servers spread around the world (a CDN). We measure from Seoul, so we read the clock of the copy that answers Seoul, which may not be the one that answers you, and we can't see the clock of the system behind it that actually decides when the sale opens. In our measurements these front-end clocks have been accurate, but treat a reading for a global site as a strong guide, not a guarantee.

Try it: type a site's address on the home page and you'll get its server time in about 15 seconds.

Server time guides

• When exactly should you click for a ticket sale, drop or class registration?
  A step-by-step plan from the day before to the opening second: how to find the exact click time from the server clock, why reacting to the clock makes you late, and why clicking a few seconds early is a gamble.
• Does internet speed matter when you click at the opening second?
  Is slow Wi-Fi why you missed out? How long your click takes to reach the server, compared with your reaction time and with how far off server clocks can be.
• Waiting rooms, draws and first-come sales: when click timing matters
  Not every sale rewards the fastest click. How first-come sales, virtual waiting rooms and draws decide who gets in, and where the exact server time still helps.