system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do doctors perform 20+ hour surgeries? Don't they get mentally and physically exhausted?

I wouldn't want a tired doctor performing surgery on me. Do they get rest cycles with other doctors? Do they have places where they can "pause" the surgery to take a nap?
gpt
Most surgeries (when things go to plan) take around 30 min-2 hours. Some major surgeries e.g. a liver transplant might take ~6-8 hours. 

20+ hour surgeries would be exceptional e.g. conjoined twin separations where you actually need multiple different teams e.g. plastic surgeons, neurosurgeons etc.

Usually surgery is a very controlled situation so it would be theoretically possible to take a break. It might be reasonable (e.g. 20-30 min in a 6+ hour surgery) but you don't want to leave the patient open/unconscious too long. 

In most specialty surgeries you would have someone else who can take over for some of it.