It would seem easy enough to run a five kilometer race in a desired time.
Read this entry in the TriSaraTops blog. She shares some "lessons learned" from a recent race she ran at this distance. A cross country runner shared some valuable insight with her to help her focus more effectively on this distance.
In a shorter race, the early part should be automatic, while the later part is where you can "kick it in".
Food for thought the next time you are looking to run this distance.