Question
Assalamo Alaikum
I want to know about Madde Lazim ,Madde Munfassil, Madde Muttasil how long we can pronounce it?

Answer
Wa alaikum assalaam wa rahmatullahi wa barakatuh
Medd Laazim, is lengthened 6 vowel counts, meaning you multiply the timing of one vowel count in the speed you are reading time six, or a medd letter times three. 
For Hafs 'an 'Aasim by way of Ash-Shaatibiyyah, (the way the majority of Muslims in the world read), Al-Medd al-Waajib al-Muttasil and Al-medd al-Jaa'iz al-Munfasil are both either  four or five vowel counts.  They both have to be equal four and four or five and five. 
In Tareeq At-Tayyibah for Hafs (advanced students), there are different counts for different turuq. 

Please see the following links for more information:
http://www.abouttajweed.com/the-mudood-the-lengthenings-/the-mudood-lengthenings-part-5.html
http://www.abouttajweed.com/the-mudood-the-lengthenings-/the-mudood-lengthenings-part-6.html
http://www.abouttajweed.com/the-mudood-the-lengthenings-/the-mudood-lengthenings-part-8.html