my personal record was 8 hours, in-between a two stage dental procedure. i had an appointment and the second dentist got involved in an accident and couldn't make it but i couldn't leave because my tooth was half destroyed and someone had to pull it out. they also didn't give me a definite time to come back, and just said to wait and see if we can squeeze you in between patients, and the pain was too much to survive the 90 minute metro ride back home.

so i waited for 8 hours, suffering in a metallic waiting seat, until some asshole dentist begrudgingly broke my jaw bones and made my lower face swollen and purple for several months while complaining i was making him late for his gym session. that was definitely one of the days of my life.