in the fifth month, on the tenth day of the month, which was the nineteenth year of the reign of King Nebuchadnezzar

Nebuchadnezzar had been king for eighteen years, four months, and nine days. This is the fifth month of the Hebrew calendar. It is during the dry season. The tenth day is near the beginning of August on Western calendars. (See: rc://en/ta/man/translate/translate-hebrewmonths and rc://en/ta/man/translate/translate-ordinal)