# Time zones


> Every screen evaluates its schedule against its own local time, so 9am means 9am in each city. How to change a screen's time zone, and when not to.
Every screen evaluates its schedule against its own local time.

Schedule a playlist for 09:00 and it starts at 09:00 in each city it is assigned to, not simultaneously everywhere. For most signage that is exactly right, and it means you do not think about time zones at all.

## Where a screen gets its time zone

From its setup. A screen keeps that time zone until you change it, and you can change it if the screen moves.

## When you want the opposite

Occasionally the point is that everything happens at once: an all-hands, a countdown, a company-wide announcement timed to the minute.

For that, set every screen involved to the same time zone. They then share one clock, and a schedule fires everywhere together regardless of where the screens are.

Doing it per screen rather than globally means you can have both: a synchronised set for the announcement, and everything else still running on local time.

## Clocks have to be right

A screen keeps its clock over the network, and a screen whose clock is wrong runs your schedule at the wrong time. See [Configure time servers](/docs/screenlyos/networking/guides/configure-time-servers/) if a screen cannot reach one.