The mosque is open all day except for the prayer times that vary according to the position of the sun. Please, take note, that proper attire and several other rules related to Islam religion are to be respected.
Wikipedia https://ko.wikipedia.org/wiki/서울중앙성원
More information on visitseoul.net http://www.visitseoul.net/en/article/article.do?_method=view&art_id=46422&lang=en&m=0004003002027&p=03
전화 +82 2 793 6908
주소 140-895 39, Usadan-ro 10-gil, Yongsan-gu, Seoul, South Korea
좌표 37°32'0.064" N 126°59'50.932" E