I know it happened on September 8, 1966, but I would like to find out the exact UTC time. According to Wikipedia,
The first regular episode of Star Trek, The Man Trap, aired on Thursday, September 8, 1966 from 8:30–9:30 as part of an NBC "sneak preview" block.
Unfortunately, this information is insufficient, since I don't know the time zone.
Edit: As DJClayworth kindly pointed out, Canadian CTV network aired it two days earlier, on September 6. I am only interested in NBC broadcast, since it is a bit more well-known.