Anytime is good, the prefer the evenings but rain or wind certainly does not discourage them at all. You might want to open up one of their dams a bit and then ambush the toothy buggers when they return to repair the damage. Try to make a head shot on them if at al possible, a beaver not hit well will go a long ways, thrash around and sink. You need to crackem good in the head to stop them dead in the water. Good luck