If this isn’t your timezone, you can look it up here.
Timezones like “EST” are ambiguous. EST could mean US eastern time, Australia eastern time, or Egypt time; many other abbreviations are ambiguous, too. Then there are daylight saving rules and other smaller differences. And then they change… Timezones just, generally, suck. So Sopel makes use of much more specific names, which refer to a database that has all these complicated rules taken care of.