How long is the Horizon Forbidden West Burning Shores DLC? The answer to that question really depends on just how involved you want to get, but there's essentially two different answers to "how long to beat Horizon Forbidden West Burning Shores DLC" depending on whether you try to tackle all of the optional content in the new DLC or whether you focus on the game's critical path.
According to reports online, Horizon Forbidden West Burning Shores takes roughly 8-10 hours to beat the DLC's story or critical path while a full completion will run players 15-20 hours. We are still playing through the game ourselves, so this is just based on reports, and we will updates further with our own findings later.
In general, Horizon Forbidden West's Burning Shores map looks to be about a third of the size of the main game's map, so that amount of time to complete it seems fairly reasonable. The new DLC also includes its own variety of collectibles and secrets in addition to four new machines.
One thing that does complicate the question at the heart of this article is the fact that any players interested in taking on Horizon Forbidden West Burning Shores first needs to complete the main storyline of Horizon Forbidden West, which is itself a daunting task. The new DLC is then made accessible through a story mission that begins in Tilda's Mansion. In other words, don't expect to hop into the DLC first thing if you've not quite wrapped up Horizon Forbidden West yet.