What do you mean by the first three and the last four?

The first three days and the last four days mean that it is best to burn paper in Tomb-Sweeping Day.

One theory is that there are many people burning paper on graves in Tomb-Sweeping Day, and the coins burned are easy to be lost. Another way of saying this is because the day before Tomb-Sweeping Day was the "Cold Food Festival", which commemorates the retreat of famous officials in the Spring and Autumn Period and the Warring States Period. On this day, it is not allowed to make a fire and eat cold food.

In the Western Han Dynasty, Qingming first appeared in the form of solar terms. At that time, Qingming was just a solar term, and there was no custom of ancestor worship. During the Wei, Jin, Southern and Northern Dynasties, the Cold Food Festival became popular, and our present Tomb-Sweeping Day is also inseparable from the custom of the Cold Food Festival.

Legend has it that the Cold Food Festival was set up to commemorate Jiexiu, who lived in seclusion in Mianshan because he didn't want to accept Jin Wengong's reward. Jin Wengong couldn't find it, so he let Yamakaji go, and Jiexiu died. So Jin Wengong set up a cold food festival on this day, forbidding people to use fire and eat cold food.

Tomb-Sweeping Day's Theory of "Left Five and Right Six"

Some people say that "left five right six" represents time, which means that you need to go out to the grave after five o'clock and before six o'clock in the morning. Some people think that it is enough to finish worshipping before 3 pm. In fact, in my hometown of off-year, I can only go to the grave or visit the sick in the morning. After noon, it is not the time to visit the sick and worship the ancestors.