I recall it took a few days for the landing footage to be released. When considering having to wait, I can remember finding an official NASA publication about Viking's Mars surface pictures from 1976, with the explanation the lander cameras recorded data at the exact speed that could be sent back to Earth back then (the tape recorders of the time were considered incompatible with the heat sterilization the landers went through) and would take several minutes to form a still image, one column of pixels at a time.