You're right about the encounters; I was misremembering what I'd written vs. what the rulebook suggests. Six is the minimum. I don't know your experience level with Shadowdark, but none of the encounters on the random table require combat, though they can often lead that way. I'll confess that I was running out of time (and thought I was running out of space) when I tossed my mostly complete list of bespoke encounters, descriptions, and rules for the gulch section and compressed it down to use the table included in the rule book. As I type that now, it's obvious that by "glossing over" the gulch, I zeroed-in on the destination when travel through the gulch in my assigned title might have worked better as the main focus.
Walking will take more than one hour extra, however, the seventh hour encounter is prescribed (and not a random roll) as it matches up with the timing of sunset and the emergence of the shadows; I should have made it a little more clear that you'd still be walking after the seventh hour. Going by the rulebook, one Arduous six-mile hex should take eight hours on foot; with no encounters, horses (or other mounts) probably would make it in four. My original custom encounters included a fair number that would attack the horses directly (e.g., gopher holes and worse, leading to a party traveling only as fast as its slowest member) and rules for adding time to the clock if you spent too long dealing with an encounter. Lose one horse, and you're definitely not making it before nightfall. Tarry too long with an encounter, and you'd lose an hour. As I said before, I tossed it all because I was out of time and I didn't like how punitive and convoluted the whole gulch travel system was getting.
Please don't take these explanations as me being defensive; I genuinely appreciate you taking your time to give me feedback. Typing all of my thoughts out is helping me see even more rough edges that should have been sanded off. Thanks for being a sounding-board.