Time of day means very little when doing research at sea.
Research ships are expensive to operate so we all try and get the most out of every minute we are at sea. In addition to using the CTD data to map where the plumes are, most of the scientists on board depend on the CTD to collect water samples for their analyses. Much of the water is filtered through very fine filters to separate the tiny hydrothermal particles that are suspended in the seawater. After collecting various small samples of water from each of the 20 liter sampling bottles on the CTD, the bottles are moved inside the ship and installed on a rack. Each bottle is pressurized with nitrogen gas, and an outlet tube is attached to a Teflon filter holder containing a small filter 37 mm in diameter.