It is set according to the targeted audience’s local time, and not according to UTC. So, if you set the campaign settings from 10:00 to 19:00, then a user from New York will see the campaign from 10:00 to 19:00 EST , and a user from Los Angeles from 10:00 to 19:00 PST.
​

You can also select the exact timezone you would like the users to see the ads, so even if there are several time zones in the country, the scheduling will be applied according to the selected timezone.