You can't manage time.
The word "manage" implies control. A big no-no in my book is also the phrase:
Again, "manage" implies control. Let that one sink in: by saying "manage people" you are saying that you really wish to control people. Nice concept that fails, in epic fashion, when faced with reality.
You can not control people. Never, ever.
You may think you control someone, but that's an illusion. At best, you may temporarily have some sway over someone's behavior, but that will not last. Just ask any parent. I'll also add that you may be allowed to think you control someone's behavior, but that's solely at the discretion of the person you think you are controlling.
The above is why I much prefer the term:
"Lead" isn't about controlling behavior of others, it's about encouraging the behaviors required for mutual success in an endeavor (any endeavor). Think about it: Generals don't "manage" armies, they "lead" them.
So what can you "manage"? Well you can manage a process, for example. You can manage a piece of machinery as well. As noted above though, I don't necessarily think you can "manage time", at least in the strictest sense of the word. Why? Well time is a constant, relatively speaking. It will occur, and at at rate you can not change, regardless of your attempts at control. The notion that you can "manage your time" is, as a result, a fallacy.
It all comes back to control, and the one (and I will note only) human you can, in fact, control is you. You can manage yourself. In the end, it's not "time management" that some folks lack, but rather it's simply self-discipline. I suspect that in the world of soft-sounding business speak "better time management skills" sounds better than "better self discipline". We like sounding better, don't we? But sometimes in our efforts to not offend others we end up muddying our intent. Sometimes a bit more precision in language would serve us all a little better.