Schedule 17 Application for the OOC station (20/0012/HS2OPDC) contains some indicative timescales and indications of the construction method/sequencing.
Here's a link to the "Written Statement For Information"
http://planningregister.opdc.london...heSeqNo=1396789485&theApnkey=9397&theModule=1
Here's an excerpt from the "construction programme" of said document, though these things tend to be highly fluid...
There is no "Chiltern Station" - AFAIK it was only ever a crayonista dream. It won't be possible in future without knocking down part of Wells House Road or some very expensive and disruptive retrospective grade separation.