Rod Serling invited any viewers to submit a script. He was flooded with over 14,000 scripts, and he actually got around to reading 500 of them. But only two were any good, and he couldn't use them because they didn't fit the format of the show.
All episodes in Seasons 1, 2, 3 and 5 were thirty minutes in length. Episodes in Season 4 (airing from January to May 1963) were one hour in length due to CBS' switching the show's available time-slot where only an hour could be taken.