I'm not sure how this response relates to my post, but since you asked: Joseph waited until after Jesus was born. Note that the fulfillment of the prophecy required a virgin to both conceive and give birth:

Matthew 1:22-25 Now all this was done, that it might be fulfilled which was spoken of the Lord by the prophet, saying, (23) Behold, a virgin shall be with child, and shall bring forth a son, and they shall call his name Emmanuel, which being interpreted is, God with us. (24) Then Joseph being raised from sleep did as the angel of the Lord had bidden him, and took unto him his wife: (25) And knew her not till she had brought forth her firstborn son: and he called his name JESUS.