the answer is...WHO KNOWS!
bbc HD has just increasesd its hours and is not transmitting 9 hours aday...the maximin the BBC Trust will allow it to do so.
it may be awhile before any bbc channels go 24/7 broadcasting...especially when BBC HD already show a mix of bbc1 2,3, and 4 programmes in HD.
also, with one HD channel they do not have to show any regional output, but if they do have BBC HD channels for all bbc regions and channels then these alone will take up half of astar 2d's frequencies - bbc2 have a few regions (like wales, english, NI and scotland)
and if / when they do their reception will depend on which frequencies they use - a vertical one like the current bbc hd channel, or a horizontal frequency like bbc uses.
mind you , there is a nice spot around the south of valenica, i was getting bbc2 on an 1m dish at about 2pm in the afternoon, and someone else around there also gt bbc2 24/7 on his 2.4m dish...just ghoes to show how the signals vary in such a short area.