Introduction Providing an accurate estimated time for patient handover in the emergency department (ED) can be difficult from the scene. The time taken to offload a patient from a conveying ambulance and transfer into the resuscitation room is often not considered within the estimated time of arrival (ETA). The aim of this study was to assess offload times for pre-alerted patients conveyed by a UK Helicopter Emergency Medical Service (HEMS) by air and road ambulance. Methods A prospective observational study was conducted at The Air Ambulance Service (TAAS) from August 2022 to February 2023. Consecutive emergency patients who were pre-alerted to hospital and arrived at an ED or Percutaneous Coronary Intervention (PCI) centre with an escorting air ambulance crew member were included. The offload time (time between hospital arrival and handover of the patient) was measured using a stopwatch. Results Data was available for 228 patients arriving at 18 hospitals and 6 helipads. The median offload time by road ambulance was 2 min 34 s. The range of helicopter offload times was from 4 min 20 s to 21 min 37 s, which mainly depended on the location of the helipad. Conclusion An additional 2–3 min should be added to the ETA by road ambulance. There is large variation in helicopter offload times depending on the helipad location (secondary/offsite helipad taking longer than a primary rooftop helipad or primary same-level helipads). HEMS services should review their own offload times at local sites to be able to provide a more accurate ETA.