We moved into our current house early last summer and have between 10 and twenty mature trees. From my recollection there was an early drop in August or September that were not very good but the trees still had significant pecans on the them. We had another drop in mid to late November and they were very good. Another factor is they seem to alternate years on producing at least the native ones do not sure about the improved varieties. Of all the trees I have only one seems to be producing this year.

I always just picked the nuts off the ground and the husks came off easily or had already gone. Nuts just drop out of the husks. The husk opens up and the nut becomes apparent and they start to drop. Sometimes the husks stay on the trees. longer.. Here's a simple link below.

Harvesting Pecans

Once the shucks start to crack open even the slightest amount you can go ahead and pick them off. Remove the shucks and spread them out to dry for a week or so and they will not be bitter any more.

Various insect or shuck issues will cause some nuts not to fill correctly. This damage occurs in the 4 to 6 weeks prior to the shucks opening.