Time of day plays a tactical role in Warcraft III. Night and Day times bring with them certain advantages and disadvantages. Orc and Human units regenerate during the day and night while the Night Elf units only regenerate during the night. Certain Night Elf units can become invisible at night. In addition, during nighttime, some Creeps go to sleep, and the sight range of your units decreases.

Day/Night Indicator
At the top of your screen, you will see a small orb that will transition from a sun to a crescent moon. This timer notes the passage of time from day to night in Warcraft III. There are 8 circles which indicate the time ticks for either day or night. Once all of these circles fill up, the time will change from either day to night or night to day. There will be a bluish glow for night, and a yellowish glow for daytime as well. When the day turns to night, you will hear a wolf howl and immediately notice that your field of vision is smaller on the minimap and screen.

Sight Range
The Day/Night Cycle affects the sight range of units and buildings. Units and buildings see more during the day and less at night. This makes scouting during the day and troop movement during the night ideal. The Night Elves can research Ultravision which allows them to see just as well during the Night.

The sight radius of a Peasant just after dawn.

The sight radius of a Peasant just after dusk.

Health Regeneration
Heroes always regenerate during night and day. The Day/Night Cycle affects the health regeneration for normal non-Hero units. Orcs and Humans units regenerate during the day or night while the Night Elf units only regenerate during the night. Undead units regenerate during both day and night, but only while on the Blight.

Spells
Some spells are connected to the Day/Night Cycle:

Shadow Meld - Many Night Elf units are invisible at Nighttime. A Shadow Melding unit is only invisible when she is not moving/attacking. A Hero Item exists which gives a Hero the Shadow Meld ability at Night.

Night Elf players can also use the Moonstone item available at their Ancient of Wonders to turn the day into night for a short period of time. This will allow them to regenerate health and allow the Moon Wells to regenerate besides giving Shadow Meld to most female units. During that period of time, the Day/Night Indicator will have a purplish glow indicating that it is modified.