A friend mentioned a film they'd seen a few years ago about people who travelled through time to fight demons (live action, in English, probably since the mid-2000s). Does anyone recognise this description? She thought Shia LaBeouf was in it (which would suggest it was in the last ten years), but I can't spot anything matching the description in his filmography.
Bit of a longshot, but could it possibly be Constantine? It came out in 2005, stars Keanu Reeves with Shia LaBeouf as his plucky sidekick, and they spend a fair bit of time fighting demons.
The time travel thing doesn't quite happen, but there are a few scenes of "Hell" which looks like a post-apocalyptic LA. Lots of broken buildings and rubble everywhere, etc.