On which day does the "Sanfu Patch" start?

The application time for the Sanfu Patch is generally determined according to the "Sanfu" period in the lunar calendar. The patch is typically first applied on the first day of the Initial Sanfu (Chu-fu). The Initial Sanfu marks the beginning of summer and usually starts on the third Geng day after the Summer Solstice, lasting approximately 10 days. This is followed by the Middle Sanfu (Zhong-fu), during which the patch is applied on its first day. Depending on the year, the Middle Sanfu may last either 10 or 20 days. Finally comes the Terminal Sanfu (Mo-fu), when the patch is again applied on the first day. The Terminal Sanfu is the final phase of the Sanfu period and usually lasts about 10 days. It should be noted that since the date of the third Geng day after the Summer Solstice varies each year, the exact dates for the patch application may differ annually.