Julius Caesar is alleged to have completed a 25 mile double circumvallation (11 miles inner, 14 miles outer) of Alesia in 30 days, with approximately 50,000 men - though at all times, of course, some of those had to be on guard duty. This circumvallation would have been a 8 foot or so ditch in front of a similar mound, on which a 12-15 foot wooden wall was built, with fortified camps acting as keeps and with towers at regular intervals.
If we assume half the men on guard duty at a time, with 12 hour days, that is
5,280 * 25 = 132,000 feet of fortifications
25,000 * 30 * 12 = 9,000,000 man-hours
9,000,000 / 132,000 = 68
labour-hours per foot of fortifications.
Other than the fortified camps, which would have been assembled initially with materials from the Legionnaires regular pack, all materials would have been manufactured for single use at this one location. Most of the artillery (catapults, mangonels, and such) would likely have come from the Caesar's baggage train. Also the head count is strictly fighting men, and camp followers capable of assisting in the construction might have been an equal number - though none of them would have had to provide guard duty. This provide an upper limit to accompany the lower limit above, of perhaps 200 labour-hours per foot of fortification, giving a estimated range of 65-200 labour hours per foot of fortification.