When do you need the text

The index cannot be compiled before the text is complete (including location of illustrations, tables, figures and diagrams).

Unless the index is to be embedded, the text needs to be in page proof format (ie typeset into the layout that will be published) so that the page numbers recorded during the indexing process will be the actual pages where the indexed text will be found in the final publication.

I therefore need to have the proofs towards the end of the production process but allowing me time to produce an appropriate index. For an average book this will be around 2 weeks before the index needs to be typeset.