Even though the Timber rattlesnake is notoriously vicious and is known to possess an intemperate disposition...
Jason, I wouldn't be to worried about receiving a bite from a Timber from their cover.. The snake will more than likely pull farther into its hole and retreat from you once it sensed your presence. Timbers are a very shy animal and don't respond very well to human interaction. They are more likely to flee from you than give you a bite.