When will the couplets on the upper beam be posted?

The couplet of Shangliang is selected at around 8-9 am. The function of top beam couplets is Naji. In the whole building process, the upper beam is the most important and the most exquisite. When the house is about to be built, before the main girder is erected, we should choose an auspicious day and a sunny day to erect the girder. On this day, Shangliang will sacrifice to God, set off firecrackers and put couplets on the top beam. Its main function is Naji.