I can’t find an explicit statement of what constitutes a wilderness exploration turn in 1E, although counting time in days is implied in the DMG.
If we’re talking about Pharaoh, however, which was originally created in 1977, before the rules for 1E were complete, then I think reference to the “OD&D” rules are certainly in order. Volume 3, Underworld & Wilderness Adventures has an explicit statement that a wilderness exploration turn equals one day, which is what I’d use in this case, given that 1E doesn’t seem to contain any statement that overrides this.
This will yield about four encounters over the course of a roughly 22 day journey.