Time management is the art of simply being on time. This includes delivering things before deadline as well as being on time for work and meetings etc.
This is achieved by managing your time every day and being organised enough to stick to the schedule you have set out to follow.
If you are in a job but haven't mastered time management, you will often find that you are fallen behind on projects. This not only impacts you but your co-workers as well —and no one likes being unable to do their job because someone else isn't organised enough.
Other than keeping friendly with your colleagues, proper time management takes pressure off you and ensures that you don't end up doing most of your work at the last minute. This can lead to a lesser-quality end product while you know that you can do better.

This can be quite a difficult skill to maintain, but not a difficult one to pick up. Observe your actions for a few days — how long do your tasks usually take to finish? Which are prioritised over others? Once you have the answers to these questions you can set up a casual schedule for yourself and, as long as you stick to it, never be late for work or a deadline again