They cannot announce prior to the close of the offer what...

They cannot announce prior to the close of the offer what directors are taking up. The ASX will not allow it. Go read the listing rules.
To do that would be a breach of listing rules. The Directors are not participating in a placement nor an accelerated institutional offer, which then precludes any announcements of their participation.
They can announce it at the conclusion of the offer where they provide a summary of the institutional, retail and employee/director take up.
Further more the directors have to lodge an Appendix Y Change in Directors interest notification once new shares have been allocated to their holding.
As an aside, I spoke to IR who confirmed that there were a big enough number of people who had not received their offers by post and that the documents had to emailed and that they had to give these people a reasonable time period to consider the offer hence the extension.