My little bitch is very fit, but I'm sure she wouldn't be all that on the third night. I've taken plenty of people lamping with there "fit dogs" and they don't last a couple of hours. When I go lamping I go all night, run all game and plenty of them, no questions asked. I don't think even my little half saluki bitch would be able to do 3 nights on the trot with the way I lamp. 2 I'm sure she could manage but 3 would just be pushing her too far, a days rest and she would be ready to go again.
Edited to say by all game I mean rabbits and rats, obviously