Time for the rabbit to reach the finish line: 7.5+0.3=7.8 (hours) (0.3 is one third of an hour, that is, 20 minutes).

Time required for a rabbit to complete the race: 30/30= 1 (hour).

Sleep time of rabbits: 7.8- 1=6.8 (hours) =6 hours and 48 minutes.