Starting an off delay when input transitions 0 to 1 but not react when 1 to 0

Really sorry if this has been asked a thousand times but no luck searching the forum on this. I need to start an off delay timer when an input goes from 0 to 1 but not react when the input returns to 0 which may be before the off delay has elapsed or after the off delay has elapsed. Any ideas would be most appreciated. Thank you