A journeyman was paid for each day of his work, as opposed to some master craftsman who would be paid after he has completed a project.
Let's explore the etymology:
Journey: A day's work (from mid-14th century), from Latin diurnus, "of one day".
So, a journey-man was initially a man whose work was measured in days and paid for accordingly.
This initial sense of the word turned somewhat obsolete by 1816, judging by this dictionary entry:
Journeyman: a hired workman; a workman hired by the day. They were called journeymen that wrought with others by the day, though now by statute it be extended to those that covenant to work in their occupation by the year.
Another quote (Two Carpenters, 2006):
A journeyman was a day-wage laborer who usually worked under the general direction of a master.