Of course, time is real (not an illusion). But it is likely that the “perception of how fast time goes by” may be relative. For example, a day in a specific Deva realm corresponds to many years in the human realm. See “Visākhā Sutta (AN 8.43).”
Regarding the discussion of Time, I was thinking about the incentive of ending the rebirth process while pondering the length of a mahakappa (4 kappa). Apayas exist for only 1 kappa which means for 75% of time beings are in the Abhassara Brahma realm where suffering is minimal. Of course 1 kappa is utterly long and suffering in the apaya for billions of years would be insane. But it seems like even though the lifetimes of higher realms are long from our perspective, it isn’t as long from the perspective of beings that live there. So it is safe to say that the majority of “time” is spent in the apayas in the rebirth process.