I think that it is a very good idea. I regularly take a nap on very long sectors, and, in turn, allow my F/Os to do the same.
My Company also thinks that it's a good idea.
My boss (who writes the SOPs) also thinks that it's a good idea, but steadfastly refuses to issue an SOP or even guidance material on the matter - WHY?
Because the regulatory authority DO NOT think that it's a good idea, and would immediately issue a compulsory instruction banning it if the company acknowledged the practice. Then we could never take a snooze.
Unfortunately there are those amongst us who require an SOP or guidance material for just about everything, sad sad Pavlov's dog cases. My advice to them is to go take a snooze in the corner.
Regards,
Old Smokey