I get that perception of time changes (subjective), but I don't see how objective time (e.g. the clock moving at the same pace no matter what) can change.
To a great extent it is the subjective experience of time that I'm referring to. But there are also other more mysterious experiences of time that are not so easily explained. Such as time slowing down during a traumatic or dangerous event such as a car crash or some violent encounter. This is very commonly experienced and is the person's consciousness actually slowing down their direct immediate experience of time passing, to the point where they can actually perform some action that would otherwise have been impossible if the time had passed in what we consider normal speed.
Another common experience is a great acceleration of time such as in near death experiences where people see their whole life "flash before their eyes" but yet experience the details of it. There is also how we experience time during sleep, where several hours pass in what we perceive as mere moments...or dreams that seem to go on for a very long time but sometimes occur in just the last minute or two of sleep.
I have had only 2 "psychedelic" induced experiences in my life, but in both of them I experienced a profound altering of time...including even time going backward.
So I'm just saying that even though it may all ultimately be subjective, there is a real mystery in how we experience time through consciousness...but the real mystery is consciousness itself.
I can't remember who said it or wrote it, but "time exists in eternity and eternity exists in time".