As soon as you create them your products can be seen/purchases through a provided link. When you hear people saying that their products aren't 'available in the marketplace' it basically means that they are not searchable yet. This is because of indexing, not uploading. The "marketplace" is basically a giant database - your store doesn't have the ability to access it directly.. every day, maybe even several times a day, the database(s?) of newest products will be merged with the existing database, when it gets to you, your product with become publicly searchable. When there's a lot of activity these merges might take a while.. if something doesn't merge quite right, there might be delays.
Just remember that as soon as you create it your product is accessible (with a few exceptions on products that require pre-approval) - if you go out and promote it, people will be able to see it. You just won't get random search hits on it until it's indexed. So go forth and create.. just don't forget to go forth and also promote..
