Every one his day— Schultens has shewn, that the word יומו iomo, imports his birth-day. So ch. Job 3:1. Job is said to have cursed his day; i.e. the day of his birth. The verse might be rendered, And his sons had a constant custom to make a family-feast, every one on his birth-day; and they sent and invited their three sisters, &c. Herodotus informs us, that the Orientals in general, and the Persians in particular, were remarkable for celebrating their birthdays with great festivity and luxury.
Related Commentaries of Job 1:4
Job 1:4
4 And his sons went and feasted in their houses, every one his day; and sent and called for their three sisters to eat and to drink with them.