Did the first "elusive target" mission last night with 12 hours to go, I was genuinely panicking all the way through it. (I'd put this in spoiler tags, but the window for doing it has passed, now!)
I took an hour, once I'd got inside, just walking around the entire mansion, trying to find the "right answers". I decided I wanted to poison his drink, but I couldn't find poison anywhere (I assumed there'd be some in or around the kitchen, but I couldn't find it), and ended up stumbling onto the guy with his guard completely by accident...
So I spur-of-the-moment attacked the guard (killing him in a panic, which I'm annoyed about now) and then garroting the target, before calmly (in the game - not in real-life) walking the fuck out of there...
Really good fun, can't wait to play it again later.