I hope you haven't been unlucky to have visited Emart on a closed day because I have and it was on a Wednesday! Such a random day..
It looks like Emart in Gongdeok will be closing on the second and fourth Sundays for January 2013, which are on the 13th and 27th. As a warning, don't take this as their
permanent schedule because it might just change.
Their hours are 9:30am to midnight. The sign also reads that no transactions can be made after 24:00.
All this fuss about the closed days is between the giant supermarket chains
and the traditional markets - and the government is stuck trying to please both. So they have been imposing mandatory "closed
days" on the giant supermarket chains (Emart, Lottemart..etc) to "help"
the traditional markets.
Update (7/2013): Emart(Gongdeok branch) is still mandating their closed days on the 2nd and 4th Sundays every month!