How can pilots sleep or rest merely 1 hour after takeoff?
The military has been teaching people how to fall asleep fast for a long time and its quite doable. Keep in mind this pilot did not start working one hour ago, if he is relived after 1 hour he is likely at the end of his duty shift and may have been flying for the previous 7 hours and awake for some more time than that. Pilots hop time zones frequently so just because its daytime outside the aircraft does not mean that pilot started off his duty time in that time zone or even on that continent that day. 

The relief pilots may have woken up just before the flight and had a nice hour to relax before "going to work". 

The crew rest area is pretty nicely isolated and free of light and distractions making it an ideal place to sleep.