Waiting times are the most widely used indicator of patient flow. This project aims to analyse 24-hour variation in referrals and waiting times for patients referred to the Acute Medical Service (AMS). A retrospective cohort study was conducted at the AMS of Wales' largest hospital. Collected data included patient characteristics, referral times, waiting times and adherence to Clinical Quality Indicators (CQIs). Peak referral times were found between 11:00-19:00. Peak waiting times occurred between 17:00-01:00, which was longer on weekdays in comparison to weekends. Referrals between 17:00-21:00 had the longest waiting times with > 40% of patients failing both junior and senior CQIs. Mean and median age and NEWS were higher between 17:00-09:00. Weekday evening and nights are problematic for acute medical patient flow. Interventions, including workforce, should be targeted towards these findings.