Outlast 1 can last anywhere from 8 to 10 hours depending on the difficulty setting and how much exploration is done. On average, most players complete the game in 8-9 hours, but this can vary depending on how familiar you are with the game. On the lower difficulty settings, players can get through the game in about 6 hours.
The game starts off slowly and gradually builds up tension, introducing the player to the environment and different characters. As the game progresses, the puzzles become more intricate and the enemies more difficult.
The game consists of nine levels, which are broken up into smaller sections. Each level contains a variety of puzzles and enemies to overcome. There are also several cut scenes and dialogue sections which can add to the length of the game.
The game also features a number of collectibles which can be found throughout the game. While these are not necessary to complete the game, they can add to the length of the game, as the player tries to find all the collectibles.
Overall, the length of Outlast 1 varies from 8 to 10 hours, depending on the difficulty setting and how much exploration is done.