(I apologize for maybe annoying length or arguable content).
There are only some places people or groups and paths I’ve heard of who believed in time being as you said a mental construct that we can be freed from the illusion of (more than simple intellectually or Faithfully). Some eastern near modern paths for example. Sant mat which has things in common with sikhism, though they can argue their system and beliefs have been throughout but not recognized as certain ones or places, certain gurus, gnostics, philosophers, buddhas, pharaohs, and or other Famed and unknown ones. Which some can argue is totally unbelievable or just stealing from other places but they do sometimes provide good examples of why/where. But theres a lot of stuff that’s hard to believe with all this esoteric cosmology so, also they don’t ask to believe (at least one I’ve learned from) just do the practice as is at ones best and see its quality oneself.
The Astral Would be considered to have time still in their belief system, though extended, and so beings or that part of ourselves of that region is generally considered to last at least some times our normal life span before it starts to decay, and The Mental level ones some times more beyond that, but noting the astral and the mental work in conjunction for our ideal physical, so all are typically used when awake, though lacking full clarity and ability.
They can also have some beliefs like a part or parts of our true selves and regions are above or outside of time and dissolution or grand dissolution, and that each preceding, higher or more sourcing parts have less illusion, but at points between non illusion and illusion, various obstacles that tend to stop people or seem cool but not be Productive or Ideally effective. They tend to believe mainly there’s stuff at the mental level and or astral level blocking or fettering us from knowing and having maximum ability and assistance, and because its complexity and how it exists and acts, they think it requires experience of certain meditation with light, perception, and abstract vibratory sound, and giving up of certain actions or habits and vices or diets, and connection or initiation from one connected and aware from outside or on top of it not just most of the mental and below, to help burn the stuff up, and so generally believe in offering free initiation and explanation. They say That stuff is the reason for negative vices and action or thoughts, and doing them is clinging to it and keeps us bound in time and the decays or negativities prevalently yet inevitable in it.
Their belief of Par for what to accept for power and knowledge as the best is pretty high and unique even amidst what many’ll say sounds crazy, compared to a lot of carried common versions of groups people or paths/systems, unlike a lot who just say to keep along and to Better not do other things even if one has nothing, or ask to become reclusive or think of everyone or entities as evil or dangerous, which is hard in the modern day imo.
Its also only path/system or group of I know that believes in outside of time, or Definite illusion of time, ascention or apothoesis or samadhi (interchangeable for them about, just not about lower forms of projection with them), and belief in magick, powers, various entities and gods.
I hope anything in it directly or from searches related could help in pieces or point to more possibly.
I think varying perspectives of paths from across time are good those we don’t trust fully and those more, there’s not Really many if any resources in this study all trustworthy without research, and its not like there’s Endless seeming old to ancient resources or systems imo, only a decent amount.
that’s the new teaching of reiki not the original source.