Adam~ Tempo for me is 4 or 5 miles at 1/2 marathon pace, fartlek would be fine. Speed work is more structured say 5 x 1K at 10K pace with a 2 minute jogged recovery between each interval, it could be 8 x 800M or 12 x 400M or as Ive just run tonight 2 x 3K at 5K pce with a 3 minute interval, the possibilities are endless! My easy sessions are 1 hour, distance is how I feel I just run by time.