Is the nun saakinah (and for that matter the meem sakinaah) is slightly extended even when pronounced idhaar?

Question
As salamu alaykum
The nun is a letter of al wasat, and has a longer sakinah than the letters of ash shaddah and shorter than those of ar rikhawah. Does this mean that the nun saakinah (and for that matter the meem sakinaah) is slightly extended even when pronounced idhaar? I remember reading something similar in the lessons but I would like clarification.
Answer
Wa alaikum assalaam wa rahmatullahi wa barakatuh,
The timing of the saakin letters of , which are the letters in the group are a little longer than the saakin letters of shiddah (not shaddah), which are the letters in the group , and a little shorter than the saakin letter of rikhaawah, which are the rest of the letters in the Arabic alphabet.  The timing of the and saakinah should be the same time as the saakinah  and the , as well as the .  All of these five letters should have the same time when saakinah.  The and saakinah should not be longer than the others in the group, so one should be careful not to extend their sound more than the natural time this group all has when saakin.  
Please see:
http://www.abouttajweed.com/the-characteristics-of-the-arabic-letters/the-characteristics-of-the-letters-part-3-ash-shiddah-at-tawassit-ar-rakh.html