Winfly stands for Winter Fly In or some such. It is in August after the first sunrise. they pull out some WOs at that point and send down another 150-200 folks to help open the station up before Mainbody starts in Oct and the population hits 1100 or so. A lot of buildings are closed for the smaller winter crew, including work buildings and dorms. They need to be opened up and the season started in preparation for the huge and sudden influx of the Mainbody folks.
Most jobs start in October at Mainbody.