A schedule means nothing without a clock, and in signage the clock is a surprisingly interesting question. If you run screens in more than one city, whose 9 a.m. do you mean?
Screenly takes the obvious route: every screen follows its own local time. A playlist scheduled for 9 a.m. to 5 p.m. plays from 9 to 5 in New York, 9 to 5 in Chicago, and 9 to 5 in Los Angeles, each on its own clock, with no adjustment from you.
This sounds small, but it removes a whole category of busywork. Without it, a national rollout would need a separate playlist for every time zone, each offset by an hour or two and all kept in step by hand. With it, you set the schedule once and every location does the right thing.
Each screen knows its time zone from its setup, and you can change it if a screen moves. The schedule you write stays the same; only the local clock it runs against differs.
If you ever want the opposite, every screen firing at the same absolute moment regardless of location, you can set them all to one time zone. That is rarer, but it is there for a synchronized, company-wide moment.