MLA

Office, Great Britain. Post. Time Bill from Portsmouth to Chichester : Dispatch'd from the Post-Office Portsmouth, the Day of [Blank] 179[Blank] at Eight in the Morning ... Post Office, 0AD. https://collections.library.yale.edu/catalog/10980293.

APA, 6th edition

Office, G. B. P. (0 C.E.). Time bill from Portsmouth to Chichester : dispatch'd from the Post-Office Portsmouth, the day of [blank] 179[blank] at eight in the morning ... [Blank forms England 1790, Brit tracts]. Post Office. https://collections.library.yale.edu/catalog/10980293.