SIT's application typically opens mid-Jan and closes in mid-March.
WSG's application typically opens early-Feb ad closes in mid-March.
Apply concurrently (i.e., to both SIT and WSG within the same period).
SIT will be the ones who will first assess your academic eligibility. If you are shortlisted for and pass SIT's Multiple Mini Interviews and are offered a place by SIT in their four-year PT/OT/DR courses, and if you also meet WSG's general requirements (their PCP non-academic requirements), then MOH Holdings or Social Service Agencies (depending on your sponsoring employer preferences) will contact you for an info session to share more about the PCP + obligations with you.
At this point as a prospective applicant, you need to make sure you meet SIT's academic requirements, and then pass SIT's Multiple Mini Interviews and be offered a place in SIT's four-year PT/OT/DR course first. Without an offer from SIT, WSG cannot consider you for the PCP.