Slow time is a thing on a few Egan books were the population (of effectively immortal post humans) of some planets collectively decide to slow their internal clocks to allow some of their members to take interstellar trips without missing out too much of their original life.

The trips themselves of course consist on transmitting the mind to be downloaded on a new body on the other side.

I don’t really see the benefit. But running that slow, you might experience the heat death of the universe in your lifetime!

The idea is that you've already dismantled the stars and stockpiled all the energy in the universe, to use at your leisure. (i.e. everyone lives around black holes they can throw mass into to reap the bawking radiation). Since you have control over the last non-entropic systems, you can tune how fast the candle burns.

And you're a mind running on a computer! You were already going to experience the heat death! This is just a scheme to get the most subjective time out of it as possible. (Running slower is more efficient.)