Busy is a relative thing.
The SVI anchorages are not busy at all as compared to USVI and BVI anchorages, no matter what day of the week it is.
Also, the SVI anchorages see a lot of day-trip motor-boat activity from Del Rey, and they usually depart about 4pm. We use that opportunity to pick up a ball closer to the beach.

We've seen Salt Whistle Bay so packed in May that you can't even get in... I've never seen an SVI anchorage that way.