How do I reduce the time delay in the HC-SR501 motion sensor?
I have never used the BISS0001, but after looking at the datasheet I'd say you need to reduce R13 only.  That is, lower R13 to maybe 1k, then turn down the delay adjustment.  That ought to get you a shorter delay.
If that doesn't work, then I'd use a smaller capacitor in place of CY1.  Use maybe half the given value - that should shorten the time to about 1.5 seconds (but put R13 back to its original value.)  If that works, you can try a smaller value to get closer to whatever delay you want.  Too small may not work at all, though, which is why I suggest a moderate change as a test first.