This has been consistent for every job I've ever had.
> I'm expected to bill at least 8 hrs/day
I bet you're capable of far deeper, more intellectually stimulating and rewarding work than you're doing now.
For my next job I'll move to an inhouse position, hopefully things will be better in a setting like that.
Salary exempt is usually a losing game for developers. Crappy places will say "we pay you a salary to get the work done" and under staff and/or overwork. If it takes you 60 hours then you have to work 60 hours. But if it only took someone 30 hours they can't leave early because a) deadlines will be tightened to ensure 40+ hours or b) more work and assignments will be given.
W/O knowing anything about your situation sounds like some sort of financial services job.