Different Conceptions
There can be found a lot of different notions and concepts of “time”; this term is used in many ways — not necessarily always in connection with clocks.
Very often it is associated with terms like “past”, “presence”, and “future”. These may apply to a certain point at the time scale defined by clocks. But the underlying concept they refer to does not generally imply exact measuring; it is not about distinct periods of time.
Sometimes past and future are just kind of directions, seen from a certain spot, the time being, the presence, now. But in general, there is meant to exist an essential distinction, the two terms referring to completely different qualities.
There is an intimate relation to knowledge: the past is principally known (or at least knowable), while the future is generally (still) unknown.