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://pt.wikipedia.org/wiki/Mesquita_Central_de_Seul
More information on visitseoul.net http://www.visitseoul.net/en/article/article.do?_method=view&art_id=46422&lang=en&m=0004003002027&p=03
Telefone +82 2 793 6908
Endereço 140-895 39, Usadan-ro 10-gil, Yongsan-gu, Seoul, South Korea
Coordenadas 37°32'0.064" N 126°59'50.932" E