Very good point. And, as far as I get it, there is a rather high probability that even the “dream machine” itself is a hologram. You already saw that piece, but anyway:

https://medium.com/@senderspike/holographic-universe-fd2834e43c71

With regard to your salt cave experiment – it very much reminds me of sensory deprivation tanks and their predecessor, witches' cradle. You can also make a less extreme experiment when you close yourself in a completely dark and relatively silent room, preferably at night. It's just a matter of time (lol) until you start to see and hear “things.”

As for time, I was fascinated to find out that there are working frameworks that don't need Einstein's block universe to work.

https://senderspike.medium.com/what-time-is-now-2f3fa4262677