But even men had days of indefinite length, they did not see days as the same length, they would see some days as lasting longer than others. They had nothing to measure time with. Days did not have a fixed length. Consider Joshua's long day,
consider how we say 'the day flashed past' or 'its been a long day'.
does 'day' mean the same thing in every context? no, I agree with that part.
I think the israelites had a 24-hour average day, seems that it was measured sunset to sunset.
I think they understood that they were supposed to work six of those, rest the seventh.
Joshua did have a day that seems to be longer than the average 24-hours. measuring it from, say, sunset to sunset, I think it would count as one of the six work periods.
yes, there probably is slight variation in 24-hour length, and at least one miraculous variation. maybe that's why the israelites probably said 'sunset to sunset is close enough, work six of those.'
I think God was ok with that.