Marinetraffic.com (at least as linked from boatyball.com) shows indicators for boats all over the BVI. Some questions for those in the know:
1) do charter boats (e.g. the moorings fleet) have AIS beacons? If so, are they automatic or controlled manually?
2)  what's to explain the range of timeframes for boats shown? Some are from 18 hours ago, some are from minutes ago.

https://www.marinetraffic.com/en/ais/home/centerx:-64.550/centery:18.408/zoom:13

AFAIK, no (or very few) charter boats have AIS beacons.

The time difference is apparently the last time a beacon message was received from the vessel. I use marinetraffic.com to identify the ships that I see pass to the north of me here on Anegada.

All Moorings boats delivered in the last year should have ASI.

The charter boats tend to have AIS, but often they haven't programmed in the boat name and they just broadcast a MMSI number.

The free version of marinetraffic uses volunteers for receivers placed all around the world. When a boat leaves the reception area of any receiver its last position is kept and the timeframe just gets older. Likewise, if an AIS is turned off then the last position just "ages". The paid version uses satellite receivers as well, and position reports are not limited to terrestrial stations any more.

Here's my last 24 hours of track (I'm anchored ) : Zanshin Marinetraffic Track

Do the Moorings boats have only receivers or do they have transceivers?

I see moorings boat transmit. It is a good way for the charter companies to know where their boats are and where they've been. A transmitter is only insignificantly more than a receiver in the grand scheme of things.

They have transceivers but again only on the recently delivered boats.

I would estimate based on our recent charter that about 60%+ of the boats out there are transmitting an AIS signal. Still need to keep your eyes out, but it’s really becoming “easy button” sailing.