The only tangible empirical evidence of ‘Time passing’ is change. Time references change in two core contexts:-

1. The dimension of change. Time calibrates and indexes change and events in standard units. Hence rate i.e. miles per hour. The per hour bit is the calibration of change rate.
2. The collective ‘flow’ of change events. Time is to change-events what traffic is to vehicles….a non-specific collective term. Does Traffic actually exist? Fundamentally all that exists are individual vehicles. Does Time actually exist..fundamentally all that exists are quantum change-events.

So Time references change in two contexts…both are abstract. So the nature of Time is that it is abstract. The tangible reality is change and change-events.

(Though try telling a taxi driver late for the airport that fundamentally neither Traffic nor Time actually exist)