Brush calligraphy. Using the traditional format, the signature can be divided into two parts. Common only the next paragraph, the format is:
Time (usually not Gregorian calendar)+(%location)+author+(respect) book
Such as: "Ding Chun (Xiahuan) worships books in Gufengtang XX".
In traditional calligraphy, dates are marked by years, and months are marked by lunar calendar, not specific to a certain day.
but
Hard-pen calligraphy, if arranged horizontally, can be in a modern format: May 2020 17 XXX book. If it is vertical, it should also be in the traditional format.