WNBC thought that putting the show on in it's original 4PM time slot would make ratings magic again. The ratings they got would have been acceptable on WPIX or WOR--but WNBC, as a network affiliate, had unrealistic expectations for an off-network rerun.
After a month they moved DS to 3AM.
When the show returned to the city via PBS' WNYC in 1987, it was considered a huge hit, with the same rating it got on WNBC!