Maybe 20 to 30 minutes at the most. My hospital isn't that far away. Now when I was in the service, it could be up to a couple of hours till the Medi-Vacs could get in.
About 45 minutes. Decided it would be a good idea to do an assignment report on ambulances for school. Complete with photos, I scored an A plus. Luckily I had ambulance EMT's who were willing to participate. Would have stayed longer but an emergency call came in and I had to cut my time short.
Thankfully I have never been in one. From my house to the narest hospital is about 20 minutes, though.