Qin Yirou went to the market for some fresh produce every Friday during this hour because her son and daughter were dismissed from schools on Fridays and the three younger children, Yun Zhu, Duan Li, and Duan Ya were around too.
Ge Junjian would come back every Friday as well, so Qin Yirou would make her trip to the market that very day after picking up the young kids and dropping them home in the afternoon.
As for Yun Yi to come home from Di Yi Senior High School, he would have to pass by the market that Qin Yirou frequented each week. He had bought a bicycle not too long ago and would certainly go through the market on his way home because it was the shortest route. Hence, Yun Yi was always cycling through the market.