A reef at night is a genuinely different place to the same reef in daylight — enough that many divers who've done dozens of day dives describe their first night dive in the Maldives as one of the more memorable ones on their logbook.
What's different after dark
Many reef fish that are active by day tuck into crevices to sleep at night, while nocturnal species — moray eels hunting in the open, crustaceans, and occasionally reef sharks actively hunting in the dark — take over. Torch beams narrow your field of view to whatever you're pointing at, which changes the whole rhythm of the dive.
What to expect practically
Dive centres run night dives as a guided group activity, typically at a familiar, relatively sheltered house-reef site rather than a demanding channel dive, given the reduced visibility and navigation challenge of diving in the dark. A dive torch (usually provided or rentable) is essential.
Who it suits
Most operators prefer divers to have some logged dive experience before their first night dive, simply because reduced visibility and disorientation are more manageable once buoyancy and basic navigation are already comfortable in daylight. Ask your dive centre directly about their specific experience requirement.