That's correct for D4, but why is the GND terminal of the 555 connected to +5V? I don't see how your trig arrangement can give you the lockout you asked for when you are effectively disconnecting the 555 supply (except when the trigger is held down)? The 555 and R4 don't seem to be doing anything useful in the above circuit; the relay is simply energised as soon as the trigger is pressed.