No, not yet I haven't. But that's going to be pretty much the next place for me to go. I did see some enemy through the gate at the bottom of the castle which I'm going to look into first, and then make my way to the top. Might not be until tomorrow though. And holy crap you can stealth him? I swear I walked in stealthed but he was aware of me before I could get close. And no, I base my victory on pure luck, and I heard the garage door start to open in the middle of the fight and I knew my wife had arrived with our dinner, so it was a now or never (later) fight.
Edit: You replied while I was in the middle of my edit, so I dunno if you saw my last bit.
There doesn't seem to be a way to get accurate playtime, I just checked the save file there and nothing stamped on it but the date, suppose you just have to roughly gauge what time you put in over the last 11 days, personally I've lost count but I'd imagine it is quite a bit as I've not been playing much else.