Is the expansion of the universe caused by time?

Something called Dark Energy is now the leading theory of what is driving expansion of the universe, though cosmologists themselves are not sure what Dark Energy might actually be. However, it must be some kind of force that has properties opposite to gravitational attraction which over billions of years would be trying to collapse the entire universe back into a singularity - but this doesn't seem to be happening.

No, time is not the primary cause of the universe's expansion; rather, space itself is expanding, and the concept of "expansion" in the context of the universe refers to the increasing distance between galaxies, clusters of galaxies, and so on over time; it does not mean that galaxies are traveling farther apart through space; rather, it means that the fabric of space is stretching, which causes the separation between galaxies to increase. The theory of General Relativity, developed by Albert Einstein, describes the behavior of large-scale structures in space-time, and while time plays a significant role in this theory, it is not the cause of the universe's expansion.