Never. The freshness is part of the intrigue.
Pinky...I don't know how far out from the beginning of season your were thinking about digging them? Although I tend to agree with Mark, many times I haven't caught a coyote out of a dirt hole until the 3rd, 4th, or 5th night...sometimes longer, and they're obviously no longer fresh at that point. Like most things trapping, it comes down to personal preference and what works best for you.