How to set blend tree animations has exit time ?

I, very simple question here, I need my blend tree animations to has an exit time between each others
how is it possible ? thanks !

This can be useful?

This explain how to edit transitions between a blend tree and a motion outside the blend tree, I need to edit transition’s parameters wich are inside the blend tree itself.
I think it’s not possible an it’s strange

The parameter is proportional to the exit time. The lower the parameter, the less time to exit.