By night, when evil accidents are most terrible and least avoidable.
The arrow; the pestilence, or any such common and destructive calamity; for such are frequently called God’s arrows, as Dent. Deu_32:23,42 La 3:12,13, &c.
By day, which is the time for shooting of arrows. The sense of the verse is, He shall be kept from secret and open mischiefs at all times.