IIRC, they were working on a generic space movie parody at the time, and they re-wrote it into the star wars parody. I expect that the 7 months was the lag with publishing.
(This is based on a remembered reading of “Good days and MAD”, Dick DeBartolo’s memoir of the days working with Bill Gaines- I have the book at home and I’ll post an update if I’m wrong. 
) Also amusing is that (again, IIRC) Lucas’s lawyers sent a C&D to MAD magazine over this parody. Gaine’s response was to send them a copy of the letter the Lucas himself wrote to Gaines with a message in the margins saying “Gee, your boss liked it!” which ended the matter.
