lowest point on the line if there is one. However, the water should eventually stop. If it's truly leaking all day, your valve may not be shutting all the way and it's slowly letting a little bit of water out constantly.
Couple ways you can check. The easiest is to make sure all your water valves are off in the house and go check your water meter. If it's moving, you've probably got some water flowing through your valve. You can then turn off your water supply to the irrigation system and see if that stops the water flow.
If you've got a slow leak through your valve, there's a piece of sand or something in the seal of the diaphragm that isn't allowing it to close/seal completely. Pop the top of the valve, clean it out and replace.