Take the extra 8 hours in a day to recover following a longer workout by running in the evening! Sunday I ran 12 miles in the morning, and at this stage of fitness and age I normally find it difficult to do anything substantial the following morning (I ended up doing 8 miles on the bike rollers and 10 x 1000 meters swimming!). Then Monday after work I cranked out a respectable 8 mile run and felt halfway decent.
This works! You get 2 extra meals in addition to several hours of rest, making back to back running workouts much easier to handle. Now, the question remains what do I have left for Tuesday? Fortunately, this is a planned easy day so I can bounce back and be ready for intervals tomorrow!
(I'm searching for some scientific evidence to support this but so far have come up with nothing- not giving up though)