Here is my attempt at explaining what I think time actually is:

At the quantum level particles can be in two or more places at once. At the quantum level, every particle has its own set of probabilities for all it’s properties (spin, charge, etc.) at any given time. Liken this to the idea that every particle has two or more ‘probability timelines’ — branchings of different possibilities.

As particles interact, their sets of probabilities merge into smaller subsets (their timelines merge). For example, if particle A had a 25% chance to be in any of one of four spots and particle B had a 75% chance to be in one spot over the others, when particles a and b interact, they affect one another and share a smaller set of probable locations (skewed toward the location B had a 75% chance to be in).

We see this in quantum entanglement and quantum computing using sets of data represented by entangled particles. Ultimately all the particles of the universe are interacting with one another, and we have a single time line.

There is no multiverse. Time only goes forward and is a multiverse on the quantum scale (infinite possibilities) but singular on the astronomical scale (only a single reality).