The problem is somewhere else but I have no way of knowing where

-> 5,6 go out (6)
4 returns ???

How did I mess this? Thanks

"above", it's 21, not 20. => ?

(tests are the same in all languages. The fixed ones, at least)

In variant (3,4,5,6) (python, not sure tests are the same for different languages) when we use:
-> 3 and 4 go out (4 - their time)
-> 3 returns (3)
-> 5,6 go out (6)
-> 4 returns (4)
-> 3,4 go out (4)
The test gives answer 21, but it's possible for them to shorten time to 20, as shown above.