laser beam alarm using NE555 ?? circuit question Answered

hi all

my project idea : using laser beam and LDR to make a security alarm circuit , when the beam is cut , it will trigger the NE55 circuit for certain time (5 seconds only )

there is a lot of 555 dark-activated circuits on the WWW,  i know , but all of them are like on/off switch

what i need is one with adjustable delayed time


can you help me ??  thanks in advance