AnimatorControllerのTransitionDurationを0にする

UpdateTransitions.cs

using UnityEditor;
using UnityEditor.Animations;

public class UpdateTransitions 
{
    [MenuItem("Assets/UpdateTransitionTime")]
    static void Do()
    {
        foreach( var obj in Selection.objects)
        {
            var ac = obj as AnimatorController;
            if (ac == null)
                return;

            foreach (var layer in ac.layers)
            {
                var stateMachine = layer.stateMachine;
                RecursiveStateMachineUpdate(stateMachine);
            }
        }
    }

    static void RecursiveStateMachineUpdate(AnimatorStateMachine stateMachine)
    {
        foreach (var state in stateMachine.states)
        {
            foreach (var transition in state.state.transitions)
            {
                transition.duration = 0;
            }
        }

        foreach (var transition in stateMachine.anyStateTransitions)
        {
            transition.duration = 0;
        }

        foreach ( var sm in stateMachine.stateMachines)
        {
            RecursiveStateMachineUpdate(sm.stateMachine);
        }
    }
}

update transitions from 'Any State'

foreach (var transition in stateMachine.anyStateTransitions)
{
    transition.duration = 0;
}