The preposition since is ambiguous:
Simple Time is also used if the reference time is implicit and determined from the discourse:
However, Time↝Interval is used for adpositions whose complement (object) is the amount of time between two reference points:
The preposition over is also ambiguous:
See discussion under Duration.
If the scene role is Time, the PP can usually be questioned with When?.
Time is also used for special constructions for expressing clock times, e.g. identifying a time via an offset:
When something happened or will happen, in relation to an explicit or implicit reference time or event.