There is no schedule and these types of things are rather fluid. They just pop out just like TNT-HD. Dish has not commitment made on offering more HD Content. They did some time back make mention of SuperDish and upto 50 more HD channels. A month after they changed direction so I am not sure what there plans are.
As for DirecTV, the post about there new bird made it sound like they are going to use it for both locals and HD depending on demand. they have made some commitment to a certain number of HD channels, but I would take that with a grain of salt too.