Source for date and time of bug planting, "President Nixon, Alone in the White House," by Richard Reeves, Simon & Schuster, copyright 2001. pg 491.
"On May 28, the night the President was on Soviet television, Hunt and Liddy's men finally got inside Democratic Headquarters. Hunt had sent Gonzalez back to Miami for more tools, and he had come back with the clinking bagful of picks and pries. They got in at just about midnight, after taping one of the locks on the doors between the sub-basement garage and sixth floor. 'The horse is in the house,' Gonzalez told Hunt on a walkie-talkie. Hunt called McCord, who was across Virginia Avenue at a room in the Howard Johnson's Motor In. At 1:30 AM, McCord crossed the street, went upstairs, and installed bugs in the telephones of Larry O'Brien's secretary and a deputy named Spencer Oliver. [emphasis added.]