What seeds specifically? Small seeds don't really benefit from pre-soak and can be destroyed if soaked too long. Large, hard-shelled seeds may be soaked if you wish but it isn't required for any reason. Examples would be squash seeds, watermelon, beets, etc. for 4-6 hours in tepid water.

Dave

As Dave pointed out, it depends on which seed. The purpose of soaking is to soften the seed coat so that water can more easily penetrate to the embryo. Smallest seeds are rarely soaked. The temperature can depend on which seed too, while cold to room temperature water works for most things, there are exceptions like baptisia where very hot water which is then allowed to stand and cool may be recommended. The length of time can be anywhere from a few hours or until the seed begins to look more plump, to a week for a handful of trees, shrubs. To give you a specific answer we'd need to know which seeds....

Thanks guys, seems I am getting somewhere..

I want to plant Byrsonima Crassifolia, a tropical tree. The seed is about the size of a nickle, and very hard.

Well, I wouldn't say getting somewhere fast :)

I don't have any information in any of my propagation books for this seed. One would think from the size that nicking and soaking might be beneficial, but an online search doesn't turn up information that indicates that. Very little is available in way of germination suggestions that I find, other than sow @ 2 cm deep, and germination rate is typically somewhat low. I dont know how active the tropicals forum is, have you looked there?