Day and night hunts differ not only in the awesome visual presentation - the hunts themselves are different. Some fish only appear at night, while others "sleep." Therefore your targets will differ between day and night.
Each underwater hunt type requires its own suit and speargun types. For daytime hunts you'll need a daytime suit and a pneumatic speargun, while night-time hunts require a warmer night-time suit and a sling-type "rubber band" speargun.