The chasing for shadows that gets called the understanding of time is looking too hard, in the wrong place. It's a semantics issue (not physics, not math, and not cosmology)
1. An Abstract. Time is change. Change is caused by energy differential. It is independent of time. Change happens anyway. Time doesn't cause change! Time measures and calibrates change - so "time" is a derived abstract (i.e a measurement and calibration system)
2. A collective term. Every particle in the universe has its own change history/future. Its own, independent and unique change stream. Time can't be a "frame by frame" universal (using the movie picture analogy) as all quantum particles operate independently. Time is NOT an absolute, nor universal. BUT we use the word time as the collective term for all the change streams. Every quantum particle changes in its own stream. This might be in a "frame by frame" manner- but the universe of frames are not linked, not synchronised. There is no universal single frame of time. Time is the aggregation of all change, all change stream or all frames (depending on your preferred analogy). Time is a collective term for all change.
3. An Illusion. The earth rotation governs our lives. And our bodies change continually as we age. These two ubiquitous, constant change streams (day and night, and our own immortality) have caused the notion of time being a "thing" (a flow, a stream, a dimension or whatever) to be deeply engrained in our phsyche. Its an illusion!
No change means no time. Its as simple as that!
For a fuller explanation, please see www.thisistime.co.uk