I don’t believe that regs implementing the change are available yet – the date may be available after this month’s budget.
Last October’s analogous change (disregard of child support maintenance) came in a the end of the month – 27th.
The commitment to an October change was made in the 2008 budget ..
http://www.hm-treasury.gov.uk/d/bud08_chapter4.pdf
.. at paragraph 4.17 3rd item.
( see also http://www.publications.parliament.uk/pa/cm200708/cmselect/cmtreasy/326/326we03.htm )
We’ve updated our benefits advice software to highlight cases where there is no current HB/CTB entitlement but, all other things being equal, there would be from October.