Is there a scientific basis for saying on the Internet that couplets cannot be posted on Lunar 29.30?

There is no scientific basis for saying on the Internet that couplets cannot be posted on the 29th and 30th lunar months. It's just some customs.

Spring Festival has been the most important festival in China since ancient times. It is both festive and grand! Among them, the most ceremonial ones are pasting the word blessing and Spring Festival couplets, which indicates that life is thriving except the old and welcoming the new. However, according to folklore, the day before beginning of spring, Changchun, beginning of autumn and beginning of winter is the "last day". The ancients were afraid of fatigue and thought the four-day festival was unlucky. In the yellow calendar, the words "four days of festivals are equivalent to four times, not for large-scale activities" are usually written. The expression "absolute day" is mainly to remind people of some important days in daily life.

Therefore, there is a saying that couplets cannot be posted on the 29th and 30th lunar calendar.