With just three terminals, I'd think the contacts go between line and load terminals, and the CdS cell is in series with a ~2w resistor or resistance wire which heats a bimetallic switch. With line voltage and light applied the current through the resistor opens the bimetallic switch.
No power and/or no light closes the switch after a time lag.
The resistance from line to N depends on the resistor value and the CdS cell, and is indeterminate.
The contact integrity can be checked: at rated current no more than a 30 mV drop across the closed contacts is good, more than 100 mV is bad.