Valentine's Day in the United States is February 14th. The time difference between China and the United States is 12 or 13 hours.
The time difference between China and the United States generally refers to the time difference between Beijing time and U.S. Eastern or Western time. When the U.S. is on summer time, Beijing time is exactly 12 hours ahead of U.S. Eastern (abbreviated as E.T.) time. When the United States is on summer time, Beijing time is exactly 13 hours ahead of U.S. Eastern Time (referred to as E.T.). Therefore, the time difference between China and the U.S. is divided into China-U.S. Standard Time Difference and China-U.S. Daylight Saving Time Difference. Because China has only one time standard, Beijing time.
Expanded Information:
"It is also said that the earth is round, that the earth lives in the middle of the sky, and that its body is round and corresponds to the degree of the sky. China when the equator of the north, so the North Pole often appear, the South Pole often hidden. Southbound two hundred and fifty miles from the North Pole is one degree lower, northbound two hundred and fifty miles from the North Pole is one degree higher. East and West is also the same. (Also two hundred and fifty miles difference of one degree.)" "To set the balance of the world by east-west longitude, the longitude of the two places is thirty degrees apart, then the time difference is one eon. If one hundred and eighty degrees apart, then the opposite day and night. The purpose of this statement is slightly the same as that of the Yuan History of Zamarudin's Earth Circle." (History of Ming Dynasty - Astronomy I)