Until GTA III, in-world time in GTA games remain static, with all locales in Grand Theft Auto 1 and the Grand Theft Auto: London expansion packs taking place in the day, while Grand Theft Auto 2 can be set to be played in a perceptual night or day at the player's choosing (this applies to the PC and Dreamcast versions only; the PlayStation version takes place only in the day). Grand Theft Auto Advance is the only GTA game after GTA III that follows the same arrangement, being set in a permanent day.
In the GTA III Era, time moves at a rate of one second in real time is one minute in-game, making one in-game hour a minute and one in-game day 24 real time minutes. In Grand Theft Auto IV, time moves at a rate of two real time seconds to one in-game minute, meaning that one full day is doubled from 24 real time minutes to 48 real time minutes. Time is in 24-hour, military time in the game, (presumably done to avoid confusion) starting at 00:00 at midnight and going to 23:59 at a minute before midnight. Grand Theft Auto: San Andreas introduced days of the week to the series. The game even keeps track of months, but this is never used in actual gameplay.
Time incurs a large atmospheric impact, with both the physical and visual atmosphere of Grand Theft Auto cityscapes changing radically with the rising and the setting of the sun. Arguably, carrying out missions can be considered easier during daylight hours as visibility is increased; however, certain missions can only be initiated at certain times of day.
As time advances in the game world, many changes to the environment can occur. These changes are most prominent in Grand Theft Auto IV and include changes in traffic flow (generally more dense during the day, particularly during the "rush hour" periods), pedestrian density and pedestrian type. The shifts in pedestrian types vary throughout different Grand Theft Auto games and different districts within their environments. During the night, commonplace pedestrians such as businesspeople, shoppers and tourists will rarely spawn, and the density of homeless people, prostitutes and gang members will usually increase in more deprived areas.