Even if having an experience requires more than a single instant

You don't get it. Experiences aren't things that require time to occur - they ARE the moments of time.

and a brain could arise and persist even for a full second, with sufficient luck, within a heat dead universe

Irrelevant. The algorithm does not depend on the nature of the system that manifests it.

I am unable to understand why you can't understand this incredibly simple point. Do you imagine that the nature of the implementing hardware changes the behavior of an algorithm? Do you think a program run on a 'virtual' computer behaves differently than one run on an equivalent 'real' computer?

If I run a Java program that implements Conway's Game of Life, do you think it will behave any differently when I encode a computational system in, let's say, a hive of bees, and use it to implement that program?