Per Wikipedia, Journey to the Center of Time (1967), written, directed and produced by David L. Hewitt, is a loose remake of The Time Travelers (1964), co-written by the same David L. Hewitt. The Time Travelers, directed by Ib Melchior (of other #Monsterdon fame), also happens to be the first movie I remember seeing in a theater, back when it was released. The MST3000 riff on The Time Travelers is on Tubi, though the original film is not. The full film can be found on the Internet Archive.