It depends more on what's already submitted, though. For example, the #gaming tag has submissions at least a few days old, yet it's interesting stuff that might warrant at least a conversation, if not a real discussion.
Besides, it's not even that easy to tell when a submission was made if you're looking at the list and not the page details. This is going to sound extremely petty, but the extra click you have to make to view the "submission details" is too much of a hassle sometimes, especially considering it's set at the other end of the title/description/tag/whatever. One part is on the left, the other all the way over on the right, it's not... ergonomic.