Initiative

[TheUndeadKing]

"The smallest time available" is what usually determines whether a Cheetah catches its prey or eventually starves to death.

[ThunderTitan]

since the smallest time available is one turn, it is assumed, i believe, that creatures do not tire in one turn.

One turn is in what everyone acts and they don't start acting at the same time... so it's not necessarily the same as the period of time no one get tired in...

And it doesn't actually have to be getting tired in the usual sense, but rather not being able to maintain the pace, like cheetahs being all about bursts of speed at the end of which they might not be "must go to sleep" tired but simply need a small break.