Jamieson, Fausset and Brown on Job 1:5

5. when the days of their feasting were gone about--that is, at the end of all the birthdays collectively, when the banquets had gone round through all the families.

Job ... sanctified--by offering up as many expiatory burnt offerings as he had sons (Le 1:4). This was done "in the morning" (Ge 22:3; Le 6:12). Jesus also began devotions early (Mr 1:35). The holocaust, or burnt offering, in patriarchal times, was offered (literally, "caused to ascend," referring to the smoke ascending to heaven) by each father of a family officiating as priest in behalf of his household.

cursed God--The same Hebrew word means to "curse," and to "bless"; Gesenius says, the original sense is to "kneel," and thus it came to mean bending the knee in order to invoke either a blessing or a curse. Cursing is a perversion of blessing, as all sin is of goodness. Sin is a degeneracy, not a generation. It is not, however, likely that Job should fear the possibility of his sons cursing God. The sense "bid farewell to," derived from the blessing customary at parting, seems sufficient (Ge 47:10). Thus Umbreit translates "may have dismissed God from their hearts"; namely, amid the intoxication of pleasure (Pr 20:1). This act illustrates Job's "fear of God" (Job 1:1).