Eastern Standard Time is commonly described as UTC-5. EST is a fixed standard-time abbreviation. For actual eastern North American civil time, use America/New_York so the runtime selects EST or EDT for the date.
Use the location when it is available
For code and stored preferences, prefer America/New_York over an abbreviation or a bare offset. An IANA timezone carries the historical and daylight-saving rules for a region. An offset tells you only the difference from UTC at one moment.
Convert an epoch value
A Unix timestamp is already an instant. To show it in this timezone, keep the numeric value unchanged and format it with the selected IANA name. The clock display may change; the event does not.
const date = new Date(1700000000 * 1000);
const text = new Intl.DateTimeFormat("en-US", {
dateStyle: "medium",
timeStyle: "medium",
timeZone: "America/New_York",
}).format(date);
Scheduling note
When a meeting or job is defined by local wall-clock time, store the IANA timezone with the schedule. When it is a one-time event, store the resulting UTC instant or Unix timestamp. That distinction keeps daylight-saving changes from becoming surprise reschedules.