The ideal time to start postoperative radiation therapy (PORT) in head and neck cancer patients has been an issue of debate. In the USA, the National Comprehensive Cancer Network (NCCN) recommends initiating radiotherapy within six weeks from surgery. The six-week cut-off originated from an analysis of patients treated at Memorial Sloan Kettering in the 1970s. Shortening the time from surgery to the start of radiation is a concern for physicians and patients. An observational cohort study, including 25216 with non-metastatic stages III to IV head and neck cancer was conducted in California. The objective was to determine the association of delayed time from surgery to the start of radiation with overall survival (OS) using a National Cancer Database (NCDB). Cancer subsites included: tonsil, nontonsil oropharynx, oral cavity, larynx and hypopharynx. Intensity modulated (IMRT) and three-dimensional conformal (3DCRT) radiation techniques were included. The recommended 42 days or less delay was compared with a 43- to 49-day and a 50 days or more delay to determine the relative importance of an additional week or more of delay. Thirty-nine percent of patients had delay of 42 days or less, 19% of patients had a 43- to 49-day delay, and 42% of patients had a delay of 50 days or more. Median OS was 10.5 years for patients with a 42-day or less delay, 8.2 years for patients with a 43- to 49-day delay, and 6.5 years for those with a 50-day or more delay. In the postoperative setting, decrease in the tumour mass may result in a relative increased availability of nutrients for residual tumour cells, resulting in accelerated repopulation and increasing the risk of local failure. The multidisciplinary care team should focus on shortening delay in starting radiotherapy to improve survival. Unavoidable delays may be an indication for accelerated fractionation or other dose intensification strategies.