How long does it take to ride a horse 250 miles?

Walking at, say, 10 mph. ( probably excessive speed )

Distance = Rate * Time

Time = Distance/Rate

Time = 1500 miles/10 mph

= 150 hours/24

= 6 and 1/4 days

=================( figure closer to 10 days as horse is not that fast, needs to eat and rest and several other impinging parameters )

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Probably closer to 40 days of travel. You could travel more hours per day, and at a faster pace if you changed to fresh horses every 4 hours of so.