Well..
I started with Naismith as a base, multiplying each section by a factor based on: (a) how rocky or difficult I knew it to be, (b) darkness and (c) getting more exhausted later on.
I found the actual times for Charlie Ramsay's original round, and Pete Stack's. So I adjusted splits based on those (taking into account that both of them had navigation issues in various points).
Then I adjusted them again based on my recce times.