The LBBs give standard human travel as 3 hexes. Post-LBB versions of the game have a lot of variation in how far a human is assumed to move in one day. AD&D 1e says 30 miles, which would mean that if we interpret the LBB figure as per day, one hex equals 10 miles. Labyrinth Lord say 24 miles per day; Swords & Wizardry says 24 miles for a forced march. Using that figure would set a hex to 8 miles.
However, I'm inclined to make wilderness turns more like underworld turns. Underground, one turn of exploration equal ten minutes, and characters make two moves per turn. We're so accustomed to using "turn" to mean ten minutes that we forget it's really standard game terminology, even outside of RPGs and wargames. I see the underworld turn as having this structure:
- players describe their first move,
- referee describes what's visible from the new location,
- players describe their second move, ending their turn,
- referee describes what's now visible and takes his turn, assessing effects of movement or passing time, rolling for wandering monsters if necessary.
It's probably better to assume only six hours 0f travel per day, making one hex equal to one league, with a lot of extra time for scouting, grazing while traveling, rest breaks, and the like. This means that the rule about occupied castles being able to keep a 20-mile radius of wilderness clear of monsters could be based on camps or outposts one-day's travel from the castle, with guards traveling up to two hours away from their post as part of their patrol.
Edit: Turns out there was a one-line comment just below the section on Rest:
Scale: Assume the greatest distance across a hex is about 5 miles.So, the 3 hexes per move, two moves per day, 30-mile scale is the one that fits. Instead of the 2.5 mile league, we'll go with the 3-mile league, which makes one move equal to five hours. As an added bonus, we can limit winter travel to one move unless the party is willing and able to travel at night for the second move.