You can't post the encrypted messages before the "reveal date" because the recipients will be able to decrypt it right away.
The idea is not to let the recipients to know about using their public key until OP wants to call them to check it was signed for them.
Okay, so it's not about your second reply.
Even so, the non-recipient participants/users will have to trust the recipient of the message to show the correct message, since they wont be able to decrypt it by themselves.
Sounds reasonable enough if used together with the forum's trust system but involving trust is kind of a drawback.