Time delay for relay (turn-on delay)

http://www.circuitdb.com/show.php?cid=92

When power is applied to this circuit, the relay will not activate until a few seconds have elapsed. The parts count is very low and the circuit does not need external or regulated voltage. I used the circuit by keeping the 12V connected at all times, and switching the ground connection. Still works fine. Circuit will turn off very quickly after power is removed, but a rapid off/on cycle will have a shorter delay than expected because of residual charge in the cap. Not a big deal in most cases, though.