I had a question about how I grow my plants behind a window, and what I mean by 'direct sunshine'. Well - here it is:
Where those bright stripes are - that is what you're looking for. IMHO I'd go for at least 4 hours of that on your Nepenthes if you're growing behind a window. You get that sort of exposure with an East or West facing window - with South it just beams straight down and doesn't actually go into a 'normal' flat window. I find my plants do the best in West. Yeah, I don't think I'm giving my plants enough light judging based on this photo.
Here there's a red arrow pointing toward the intensity of light you want to have (it's striped because of the blinds), and the hypothetical position of the sun in the sky as traced from where that sunshine-line is on the other blinds (drawn in blue).
Also, a good way to tell if it's bright enough - see this dark blob? That's my finger 2-3 inches away from the leaf between the sunshine and the leaf - you should get sharp shadows if you've got enough light.
here's that finger shadow outlined in peach
here's my finger in the shot too