By justification I mean precisely how you are stopping or manipulating time given that it is a sequence of events. Altering it would be even more difficult given it'd require the precise rearrangement of all states of matter at a given time and include being able to recall all of that information at that instance you wish to go 'back to'.

And yes, you do need more justification for playing with time. Moving water (or even creating it) is much less complex than that kind of ability.

This matters because actually understanding what you are doing provides scope of how much energy something would take and how much time it would take to prepare it. As well, countermeasures can apply to specific expressions of an ability in particular.

But, as I said, this only applies in particular situations. For almost all combat it'd be entirely irrelevant. Few people are going to discuss the mechanics of an ability unless it dips into the realm of incredibly complicated. Most things are in fact very simple.

EDIT: I'm tired and may not be explaining this particularly well.