A time delay capsule has a tubular housing to be mounted within a coil in a magnetic relay or the like and has a core which is movable in the housing when the coil is energized for increasing the magnetic field established by the coil to the level necessary for actuating the relay. A spring normally biases the core to one end of the housing and a liquid in the housing retards core movement in response to coil energization, thereby to provide a time delay after coil energization before actuation of the relay occurs. The core and spring are arranged with respect to means sealing the liquid within the housing to permit easy capsule assembly and to assure precise and reliably predetermined core movement within the capsule.