Do 2 a day sessions to increase stimulus

Do 2 runs in a day runs to fit your schedule and to provide more stimulus. These sessions should be 30 minutes (Train for at least 30 minutes). Do not split your weekly long run into 2 sessions, as this run provides special stimulus that cannot be replaced by two shorter runs.

References

How Much - Shawn Bearden:
What Your Weekly Training Plan Should Look Like - David Roche