There isn’t a waiting list exactly, but you’ll want to wait until your account is fully verified before sending stock in. That can take a few weeks.

One you’ve decided on a product check that it doesn’t require additional approval before you go ahead and buy. Some categories and/or brands require an extra step of essentially asking permission from Amazon to list in that category / brand.

Amazon’s warehouses (Fulfillment Centres) do sometimes get close to capacity but they have “holding” areas where they can keep things before being available to buy. Generally though things move pretty quickly.

There is also sometimes a limit on how many of a product you can send in, especially if it’s something new to Amazon. In those cases they may, for example, say you can only send in 100. So don’t expect to buy 1000 of your chosen product and have them shipped direct to Amazon by your manufacturer / supplier.