You can send offers immediately. I've had times where a listing I had just created was put on a watch list before I'd even finished my listings in that group. I sent an offer immediately.
I suspect I don't use offers the same way others do, however. For me, they're just a greeting, with no expectation of a sale. I'm thrilled when buyers take them, but I see offers as the equivalent of meeting and welcoming a potential customer at the door of a brick and mortar shop.
