I am trying to design a circuit using 555/556 for handling a switch input with specific requirements. All the debounce circuits I've seen react to the leading edge of the switch actuation. I need a circuit that will ignore the input changes until it is stable (on) for about 250 msec. at which time the output changes state. Any narrow pulses or bouncing should be ignored. The output should stay active until the switch is released. The output can change state after switch release with any delay (0 - 250 msec.). Has anyone seen an application like this or know how to do it? TIA.