I would like to know the best time for collecting seashells, is it in the day or in the night? With big big thanks for all.

If you are collecting beach shells of course it really doesn't matter. The same shells will be lying there day or night. But if you are collecting live specimens, many species are active at night that are hidden during the daytime. Such species can often be found during the day by turning over rocks, sifting sand, etc., but at night many such species are actively crawling around and easier to see. Other species are plainly visible both day and night.
(Answer by M. Paul Monfils via the Forum)

Effectively, most of seashells go out at night. I noticed that they are mostly active just after the sunset. They do not hunt the whole night (too dangerous) and if they find their prey they go back to their hiding place. I studied them in live and in aquarium. In France, with the cowries, as soon as I turned light off, they were looking for their sponges... Some species may also be active during daytime too. And shells usually do not go out at night when the moon is full. So the worst days are the ones when the moon is gonna be full. As soon as it decrease to be dark they are active again.

I noticed that when moon is in it's full period shells may go hunting during daytime too (too angry I guess...) and so do not wait dark moon period...
(Answer by M. David Touitou via the Forum)