Yes a loop can be controlled for time of day usage via a timer. The loop activates the gate to open by momentarily closing a circuit to the gate opener. This means the loop detector will have two wires coming off of it going to two terminals on the gate opener. If you take one of those wires and run it through the relay of the timer then the timer will be part of the loops ability to momentarily close the circuit to the gate opener. So if you program the relay of the timer to be off at night, then the circuit will be open inside the timer. Since one of the wires from the loop detector is connected to the control board through the timer the loop will no longer be able to momentarily close the circuit to the gate opener. Thus the gate opener will not be able to be opened during off hours via the loop.