I waited until Packet 3. If you are confident it will come in time just don't mention that it didn't arrive. They really don't know. All they see in their system is that they sent it. You should be able to schedule regardless.
I was able to make an appointment after they had SENT it but we didn't have it, yet. It's true that they don't know when you will receive it and there is nothing on there that they will ask for- no special number or secret password.
