CREATE TABLE table_28400 ("Institution" TEXT, "Location" TEXT, "Nickname" TEXT, "Founded" FLOAT, "Founding Religious Affiliation" TEXT, "Enrollment" FLOAT, "Joined" FLOAT)

When did the institution located in Lewiston, Maine join the conference?
SELECT "Joined" FROM table_28400 WHERE "Location" = 'Lewiston, Maine'
SELECT "Joined" FROM "table_28400" WHERE "Location" = 'Lewiston, Maine'