Correct way to add single-frame transitions

I'm wondering if my experiments to create transitions that last one frame is what's killed Unity for me. So when fixed, I don't want to repeat that mistake, whatever it was! What's the correct way to create a single frame state transition? Those lovely blue graphics with their gradients showing blends aren't at all practical for such small increments!

To be particular, I have one state that changes the graphics depending on direction, and that connects to blend trees for animations. Transitions from this graphic state to the idle and walk states should be 1 frame, as also from idle <> walk states. I recall setting a blend transition time from 0.1 to 0. Is that Bad? Does 0.1 represent transition length in seconds? Is there a minimum value for this not protected in the editor?

My game is very simple 2D graphics and I don't want smooth transitions between movement states.

Thanks!

 

It appears that a transition time of 0.00 is not an immediate transition but perhaps a special case 'use clip length'. Changing the exit time to 0.01 creates the instant transition I want.