I totally forgot to dvd-rw drive. When I removed it, computer's POST delay was normal. I tried another ODD from ASUS notebook and this another drive (but same manufacturer) worked flawlessly
. There is some kind of incompatibility.
Stock ODD is Sony Optiarc AD-7700S with FSC branding and firmware 1.44. I reflashed it to manufacturer stock 1.3 FW and then to Sony 1.71 FW. ODD is still working but without any positive change to POST delay.
I will order new LG GT40N drive and hope it will work.
EDIT: I installed new ODD and everything working fine.