What are we watering here! Concrete?
Anyway, in the lower picture, that is a pressure vacuum breaker, backflow preventer. The valve on the left is the outlet, and the valve on the right is the inlet. I can't see anything in the picture that would involve the water to the house. Perhaps some more pics will clear that up.
If the sprinklers in question are at the bottom of any slope, then they will drain all the residual water in the pipes after each cycle. The solution....install the rainbird antidrainback heads.
6 hours seems like a lot, so don't rule out leaky valves