Modern signs on Saloon entry showing operating hours just a couple days a week when the girls show up to be Hostesses. I would guess the " Ghost Town" used as the set is just a tourist destination.
Modern locks seen on doorways when doors are opened, this style of deadbolt locks not in use in the 1880's.
As Mr. Buchinski reloads his pistol during the first shoot-out, his cartridges have copper jacketed bullets. Jacketed rifle bullets were in use in Europe in the 1880s, but at this time period his American pistol bullets would have been plain lead.
Hannah tries to stab the killer with a World War 1 era bayonet, which he later uses himself.
The marshal talks about calling for backup. This is police jargon from the late 20th century. He probably would have used the military term "reinforcements".
Also, the term "psychopath" was only just being coined at the time (1890s) in psychiatric circles in Europe. It is unlikely to have migrated to the American West so quickly, especially in its modern sense.