Ok - looks like I am answering my own question but found this news article which also then lead me to the project page:
http://www.live5news.com/story/31284855/parts-of-hhi-beach-to-close-for-renourishment-project
http://www.hiltonheadislandsc.gov/projects/beachrenourish/2016beachrenourish/
Seems like they will work in small sections at a time: “We are definitely open for business. The area of beach that is impacted directly at any one time is about a thousand or so feet in length,” said Scott Liggett, Hilton Head Island Director of Public Projects and Facilities.
“The area that’s disturbed at any one time is relatively small. Even though we have this area of about a thousand feet that’s closed, we will be making accommodations for folks to get to the beach by walking behind our construction area, one direction or the other,” Liggett said.
And some more info from the project page:
On average, the filling process should move along the shoreline at a rate of about 200 to 300 feet per day. Because the active work area may spread out at least 1,000 feet or more along the beach, several days of work activity will occur seaward of any one piece of oceanfront property. Although the only noise typifying the construction process is that of the bulldozers shaping the sand as it is deposited, adjacent property owners, or renters, may experience short-term minor inconveniences. The construction activity effect to any one location on the island generally lasts for three or four days at a time as the renourishment operation moves past each property within the project limits.
Similarly, as the fill placement progresses, thousand-foot sections of the beach are closed temporarily to pedestrian access. Once placed and rough-graded, however, the new beach is immediately reopened to the public.
The project page has great info including map.
Kevin