When should we expect to see sheds starting to drop in central Texas? I have never made a big effort to go look for them but want to give it a try this year.

For numbers, mid March and later. You can find a few earlier, but for numbers later is better. You can walk yourself to death to early, then loose enthusiasm when you need to go back over those spots that had nothing early.

Sooner the better before the rodents get to them.