The talk to the writer's group is the evening of 1st July. When they're trying to find the taxi which dropped off a woman at the house the night before the talk, DCI Barnaby tells Sgt. Troy to contact cab companies and find out about "the 31st." June only has 30 days.
During the opening, Gerald Hadley's voice is reading out what he is writing. He says he fired 2 35mm rounds which missed by 2 inches etc. A 35mm round is huge and the size of round used in an anti aircraft gun, and not the size to be fired from a hand gun or machine gun.