Sentence:  After a few minutes' waiting, two well-known runners, chosen for the hares, buckled on the four bags filled with scent, compared their watches with those of young Brooke and Thome, and started off at a long, slinging trot across the fields in the direction of Barby. Then the hounds clustered round Thome, who explained shortly, "They're to have six minutes' <WSD>law</WSD>." 
Meaning of the word marked with <WSD> tags:  An allowance of distance or time (a head start) given to a weaker (human or animal) competitor in a race, to make the race more fair.