Here’s the handy-dandy chart I’m using to calculate travel times for “province-level” hex-crawls in my Panzoasia Campaign. It’s keyed for a scale of “1 Hex = 1 League”, which I prefer because it corresponds to both the rate an unburdened person can travel in one hour, and the distance to the visible horizon on a plain.
Movement rates are given for various Old-School rules variations; “Classic” (including B/X, BECMI, the RC, and their corresponding retro-clones), “Advanced” 1st Edition and 2nd Edition rules, post 3rd Edition rules, and Ghastly Affair.
Time to Travel 1 League (3 Miles), by Movement Rate and Terrain
Wet, muddy, or snowy conditions shift effective movement rate one column to the right (harder). Forested Mountains, Badlands, or already Icy areas without roads will become completely impassable.
Generally, a road shifts the effective movement rate 1 column to the left (easier)
Travel through a Mountain Pass is at the same rate as for Open Hills.
A horse can be ridden at its normal movement rate for 5 hours total, before it must rest for the remainder of the day. For each hour of forced movement past 5, the horse loses 20% of its hit points (rounded up).
A horse can be ridden at a gallop (triple normal speed) for a total of 10 minutes in one day, covering a total of 1 league on a plain or road. Once 10 total minutes of galloping is reached, the horse cannot be ridden, or otherwise burdened, for at least an hour. A horse can only safely travel for a total of 4 hours in a day when it has been ridden at a gallop.
The total number of hours a person can march per day without harm is equal to their Constitution score. This includes the 10-minute rests indicated in the chart above. A forced march past that point inflicts damage equal to 20% of the marcher’s hit points (rounded up) per hour.