If the anticipated completion date in the L&I sign is a reliable indicator, then this should be the preliminary site prep activity. For context, RATR began construction in June 2006 and was completed in Jan 2009 = 30 months. October 2017 is about 32 months away. The work being done is consistent with that timeframe. The question is, how reliable is that sign?
One point to consider: Museum Towers II has not yet broken ground but the L&I sign on that site has an anticipated completion date of August 2016 (which does not seem very realistic).
http://forum.skyscraperpage.com/showthread.php?p=6910450
EDIT: W Hotel's website shows the Philadelphia location as opening in Jan 2018. I suppose if the building is completed by October, they need time to hire and train staff, purchase furnishings, and have some buffer time in case there are delays?
http://deal.whotels.com/?PS=LGEN_AA_DNAD_CGGL_TBRD Is this a new development? I don't recall the Philadelphia W being on the website before.