時刻の入力と表記

import datetime
from openpyxl

wb = openpyxl.Workbook()
ws = wb.active # ()は不要

ws['A1'] = datetime.datetime.now()
# from datetime import datetimeとした場合は、datetime.now()だけでよい

ws['A1'].number_format
>>> 'yyyy-mm-dd h:mm:ss'

ws["A1"].number_format = "yyyy/mm/dd"
ws["A1"].number_format = "yyyy年mm月dd日"