Do you mean EDCT's? Expected Departure Clearance Time...Expected "wheels in the well" time from the departure airport in order to meter traffic into the destination airport.
If the destination airport arrival rate is, say, 80, and the number of flights expected during one hour is 100, then EDCT's are issued so that no more than 80 aircraft arrive during that hour. This pushes the extra flights into the next hour, creating a ripple effect. This is why ground delay programs usually run for several hours.