The problem is that the 555 isn't really a single chip solution to this problem. It is designed to be triggered, take an output high for a preset period, then take it low again until the next trigger pulse. What you want is a circuit with inverted logic, ie trigger, delay, then output, not trigger, output, delay. Another problem is that the trigger input is specifically designed to be a momentary input, not a continously grounded one. You get odd behaviour if you take it low and keep it that way, and the behaviour changes from manufacturer to manufacturer.

You could use a 556 dual timer or two 555s to approximate what you want, but to be honest I've always found them to be a pain at best. The design is ancient, and all too analog for my taste. I would do it by programming up a PIC12C508 to give exactly the correct behaviour, but then I'm like that!

An analoggy way to do this is to use a suitable RC circuit to trigger a transistor or mosfet. The R and C are chosen to give a time constant such that the gate or base voltage goes above the switch-on threshold after the appropriate delay. The device will then stay switched on until the power is removed and the capacitor is discharged. This is pretty fast for a transistor, could be days for a mosfet without a resistor to help. Crude, but reasonably effective. A PIC is still easier, though.

I'm just off to bed, but I could sketch a suitable circuit tomorrow if it's any help.

Patrick