Falklands: No.10 record of conversation (1700Z) (MT-Haig) [pre-dinner conversation: Anglo-US responses to the invasion of the Falklands] [declassified 2012]

1800-1920 DST = 1700 - 1820Z. This document clearly states that the meeting began at 1900, but other documents, including the engagement diary, place it at 1800. The full file from which this item is taken can be seen here.

The talks took place in the PM's study, according to a Lobby Briefing at 1935, which can be read here.