Not daring to speak to this myself (since I grew up away from the oyster beds) I asked the Chesapeake Bay Maritime Museum if there was oystering on the Bay at night during WWII. Here's the answer:

"I rather suspect that some oystering was still taking place at night during World War II, but, if so, it was not legal. I believe oystering at night has been illegal since about 1865, when Maryland's oystering laws were overhauled and reenacted.

The offense of oystering at night was usually committed to cover up some additional illegal activity, such as dredging on ground reserved for tongers or dredging with a power vessel instead of a sailing vessel, or some other such offense.


Sincerely,
Pete Lesher
Curator
Chesapeake Bay Maritime Museum"

If you haven't visited the CBMM, do so. Their display on oystering is wonderful -- as is the whole place.