The study investigated the effect of perioperative circadian rhythm alteration on postoperative delirium (POD) in patients older than 60 years undergoing elective orthopedic surgery of the lower extremities under general anesthesia. Of the 277 patients included, the circadian rhythm change group (C group) was compared with the no change group (NC group) after propensity score matching. POD occurred in 37 patients (34.58%) in the C group and in 29 patients in the NC group. Perioperative circadian rhythm alteration was independently associated with a higher risk of POD (OR = 2.26; p = 0.02) and a longer length of hospital stay. Subgroup analyzes showed a stronger association in patients younger than 75 years (OR = 5.82; p = 0.001) and with better postoperative sleep quality (PSQI ≤ 8; OR = 6.09; p < 0.001). The study ran from August 2024 to January 2025 and highlights circadian stability as a target for neuroprotection.