Things that can affect it, with some wild estimates on how it reduces the 800kh:

• Processors are 10-100 times faster. Divide by 100ish.
• A common laptop CPU has 16 cores. Divide by 16.
• GPUs and CPUs have more and faster math operations for numbers. Divide by 10.
• RAM speeds and processor cache lines are larger and faster. Divide by 10.
• Modern processors have more and stronger SIMD instructions. Divide by 10.
• Ray tracing algorithms may be replaced with more efficient ones. Divide by 2.

That brings it down to 3-4 hours I think, which can be brought to realtime by tweaking resolution.

So it looks plausible!