Nick appears to be carving the Day Number into the tree branchZooming in there appears to be 17 cuts
According to True Dork Times calendar Episode 6 should be Day 14, 15, and 16.
http://www.truedorktimes.com/s32/calendar.htm
So maybe the first dark thick cut is a marker of where the Days start?
In any case it seems like this scene of Nick would be on the day 16 or 17 when they should be doing the Immunity Challenge and later Tribal Council.