According to the U.S. Department of State website, they are based in Washington, D.C., and if that's the case, you should time your phone calls along with the Eastern time zone. To make it easier (since you're probably outside the United States), you might want to utilize a free online website such as
TimeAndDate.com. That link will direct you to a website that has a "time zone converter and calculator" which takes into account daylight saving time (DST), local time zone and accepts dates from the past or the future. It's really a nice little site to have handy, especially when you need to convert time zones.