When I got my cab blasted, the guy was at it a full 8 hours. Of course mine might have been in worse shape than yours. It was mounted on a rotisserie that allowed him to rotate it to get to everything. My blaster could have done dustless blasting, but he didn't recommend it. When you add water to the blast stream, it increases the force applied to the metal and would increase the possibility of warping the sheet metal.
If you're having the whole cab blasted, I'll bet it would take at least 4 hours to do a reasonable job.
