The word "day" perhaps refers to the day when they celebrated the son's birth. But it at least refers to the idea that the sons each took a turn in holding a feast. AT: "On each son's birthday, the son would give" or "Each son in turn would give"
# he would give ... They would send and call for ... Job would send ... he would consecrate ... He would rise early in the morning and offer ... he would say
"he habitually gave ... They habitually sent and called for ... Job habitually sent ... he habitually consecrated ... He habitually rose early in the morning and offered ... he habitually said"