First of all, only REO has the permission to use this FAQ. If you see this FAQ anywhere else, please let me know at firstname.lastname@example.org .
This FAQ is for Raiden on Easy mode. It can probably get you through the Normal and Hard modes as well. If you're curious to what my time is, I'm first place with 2:58:33.
Olga - When first starting, make sure she runs right in front of you. If not, Restart. Press X and you should automatically hit her. Keep it held and you will be automatically target on her. Shoot her in the back after a second or two after you shot her the first time. She will now hide between areas, peeking out for a shot. Aim for her head. Target time: 20 seconds.