There are several schools of thought and practice about soaking your dentures when you are not wearing them such as when your asleep.
People have been soaking them in plain water, water with a little bit of bleach or vinegar in it or not putting them in anything at all, just on a paper towel.
When your dentures are not being worn, it is a good idea to keep them wet, such as in a small clean container with plain water or even distilled water.
As far as soaking them over night, this is done to keep them clean and remove any food debris, calcium and other residues from them when not being worn.
The practice to clean them very well as needed with a mild tooth paste or oral cleaner, and then when evening comes you can put them soaking in a solution with one of the better denture cleaning products on the market.  Only use a trusted product such as the Renew products mentioned above, or if you already have a favorite already.  Either way, you want a product specially made for cleaning dentures, because it will be gentle on the materials they are made of, not be harmful to you,  and keep your dentures clean and ready to use the next day.
Thank you,