I believe when the last two Spaceway's went up, it was like 4 weeks from launch time til the sats were tested and handed over to Directv and they were lit up shortly afterwards.
There has been no info on specific HD channels to be added when the first sat goes up, the assumption is they will start by mirroring the exisiting MPEG2 HD channels then start adding other known channels like National Geographic, MTV, etc..