According to the portal it is 5 days. I do understand that all flights into US are 3 days. https://usvitravelportal.com/
Hmmm, I do see that. Sorry for my "correction"! I could swear it was three days previously, but may be confusing it when we had to return test and were transiting through PR.
You are correct; it was 3 days to enter the USVI for a long time. It changed to 5 days a couple of months ago. BUT, that does not eliminate the 3 day test requirement for the US.