I do take occasional glances at my phone to see what time it is to gauge how long I have slept. I also like to have some noise playing in the background like playing a show or movie on my tablet or phone (I would use the IFE, but attaching my NC headphones, falling asleep and having them play an announcement would give me a heart attack) so I am somewhat aware of the passage of time.

Generally I find I get 5 to 7 hours of sleep straight on a TPAC. Probably my most restful as I can't be reached. Rest of the time, it's catnaps and watching videos and the occasional book or notes that I need to email out once I land.