I'm working with the HC-SR505 right now for a project and found this thread.
My application also requires a reliable PIR body detector, but very little delay. I tried nearly all the PIR modules on Amazon, but they all were either unreliable or had a delay that could not be changed.
So I have settled on the HC-SR505. It is very solid and reliable. But I needed to reduce the delay to under 1 second, and I agree with the OP that you can change capacitor Ct and get very short delays.
In case anyone else finds this thread, I created a spreadsheet to calculate the values of Ct (the capacitor that is pointed out in the photo earlier in this thread) that are required for various time delays. Here is an image of the table:
I have attached a PDF of this table, and a live Excel file with the formula to this post.
I hope this helps someone. 
--Jim
EG4001 HC-SR505 PIR Decector Delay Calculation.pdf (122 KB)
EG4001 HC-SR505 PIR Decector Delay Calculation.xlsx.zip (8.88 KB)