To answer some of the OP's other question IMHO:
Q: Why the over-books? (generalized question)
A: They may be having a snowball type effect; not really over-booked but missed one or two earlier in the week and everyone is slowing getting pushed back.
There is no snow ball effect. Its simply purposely overbooking. Why settle for 8 hours on a tech when you can get 10-12 hours for the same price? Its a piss poor game for everyone except DTV and the HSP. As a tech, if you don't play the game, then you get poor routes. On the flip side, the only way a tech can play the game is dedicating his life to the cause while doing poor quality work. The bonus: If he's caught, then he's charged back.
You won't get any calls for canceling because the tech is still suppose to "do his best" on getting the job done, even though he knows good and well he will never make it.