lifetime of sign in enrollment token in android management API

i am now researching on android management API. when i was on research i got a doubt that in enrollment tokens we can choose the lifetime of the token. But there is no way to choose the lifetime of the sign in enrollment token.

i have gone thorough the android management and i could not find the ways to set the lifetime of the sign in enrollment token or the default life time of it. 

Can anyone help me with that?

thanks!