Wear patterns will tell you right away if the toe in setting is off..

To zero the toe in where I want it, I pull off the side of the road, put a strip of masking tape accross the tread of the tires, pull back on the road using the least amount of turning to not scrub the tape off, and then drive for about 10 miles... and pull back off the road in an area where very little turning is required.

The masking tape wear will show you right away (assuming other front end geometry is correct)... and I walk the toe in accordingly... You can actually see the wear pattern walk up one side of the edge of the tread very slightly on one side or the other, telling you if it's toe'd in or out... The wear across the thread will be consistent e.g. if toe'd in too much more wear on the outer portion of the thread or, vice versa..

I've also seen if the toe in is off badly AND driving on a road with a lot of crown, the left front tire will be tend to be running straight on, and the right side tire wear showing that the tire is being dragged sidesways a considerable amount, i.e. to keep the vehicle going straight on a high crown of the road, you effectively are turning left slightly and putting all the toe in on the right front tire. It wears a lot faster...