How early should i start LST training on my autoflower to get great yield without stressing plant?
In my personnal point of view, not until the the fifth or sixth internode…
Hoping that helping you @tim245
~Al 
with Low Stress Training, you should wait till it’s tall enough to bend and guide easily to expose more secondary branches to light.
oops, @Niala, you gave a great answer! I type too slow…
No, no, my friend @kabongster 
, we are giving complementery advise, it’s a team work 
~Al
I agree with @Niala and @kabongster I would wait for the 5th node but also when it is tall enough to do so, if you have a powerful light the node spacing might be very tight and it might not be tall enough to LST.