According to imam al Jazari madd munfasil can be read for the duration of one alif...

According to imam al Jazari madd munfasil can be read with the duration of one alif. Is this correct?
Also could you tell me all the places where two letters come from the same place but both will be read and not merged into one another. e.g in soorah kafirun the word abadtum is read without the letter daal and merged with "taa". but in soorah maa'idah, ayaat 28 the word basathta is read with letter "twa" first and then also with "taa" and there is no merging. why? and also how many places in the quran does the same rule apply like the example in surah maa'idah, ayah 28

may Allah reward you with good in both lives.

Wa alaikum assalaam wa rahmtaullahi wa barakatuh,
The length of an alif is two vowel counts, and yes, for Hafs 'an 'Aasim in tareeq At-Tayyibah there are some turuq which read two vowel counts.   To read this way, one needs to know all the special words and how they are read for the particular tareeq. 

When the two letters are or mutaqaaribaan, it is not a given that when the first is saakin and the second voweled that they merge into each other (are read with idhgaam).  The two examples given in the question though both have idghaam. 
In Surah Al-Maa'idah, aayah 28  , the incompletely merges into the , meaning the characteristic of remains from the , but all the other characteristics of the merge into the .
When there is a saakinah followed by a letter , there is a complete merging of the into the .  This is wherever we find this situation in the Qur'an, and that is why we find a shaddah on the letter , an indication of an idghaam.  Two examples of this idghaam are found below:

For more information about these types idhgaamaat, and the occurrences asked about in the question, please see:

Ameen to your dua' and may Allah reward you with khair in both lives also.
Wa assalaam