How Many Days Does Nyles Relive In Palm Springs?

The most telling scene in the entire movie takes place at almost exactly the mid-way point, when Nyles and Sarah are having a campfire heart-to-heart, shortly before they have sex for what Sarah believes to be the first time.

When Sarah asks Nyles about his life before the loop, namely his job, he replies that he can't remember, adding, "Wow, it's been such a long time."

Considering that people tend to remember important details about their lives for years and even decades after the fact, it totally tracks that Nyles would have to have resided within the time loop for around 40 years for the memories to degrade to such an extent - even accepting his daily drinking habit.

As Siara said, "A lifetime of memories has passed," adding considerable gravity to Nyles' arc throughout the film.

Given that Siara confirmed the film was intended to be an allegory for depression, which has a tendency to warp the passage of time in people's minds, it's really quite a perfect - if grim - metaphor.

So, there you have it - Nyles spent at least 40 years trapped in the loop, and as Siara doesn't seem totally married to that figure, settling instead on "a lifetime," it could easily be a decade or two higher.