I have worked in automotive and the testing of a software release took about 1 month for a ~150 member team. Yes, documentation because legal requirements was as much as 10% of the human labor, but the tests ran for a month in simulated environment.
This was not a particularly large software, about .5MLOC total with 3rd party RTOS as well (not in our test scope).
The tests did find unexpected bugs, as the dynamic behaviour of the system was much harder to reason about than about the single components, and sometimes pretty weird system effect kicked in.
I'd also not trust this to small teams, this is simply way more complicated than one presumes prior to experiencing it personally.
