Daily travel time in AD&D 1e

The PHB states that the players can move their inches rate in miles in "a half day's travel". Would that imply that a full day's travel is double that number? One would assume that means 12 hours, but if you cross-reference those numbers with the DMG, you'll notice those numbers are still too low. But they do work out if you use 14-16 hours of travel per day.

AD&D 1e assumes 16 hours of travel per day.

It may not be the most realistic metric, but I like the idea that characters are spending the entire day sans rest time, traveling. The 12 hour travel rule otherwise gives characters 4 hours of downtime in which they are not sleeping or traveling. AD&D 2e explicitly states 10 hours of travel, allowing for 6 hours of downtime and 8 hours of sleep every day. Kind of a waste, I think, even if it is more realistic.