It depends on how low the state of charge is. It could easily take 8 hours or it could take an hour. No one can tell you. I fou charge it for awhile then let it sit for an hour or two with no load connected it will lose it's surface charge and you will then be able to a more accurate state of charge voltage which when fully charged is 12.6 to 12.7
You want the battery to be fully charged when storing it. If fully charged it will be good for months. I'd set it a pan or plastic tray just in case. Sulfuric acid eats everything.