Meaning of the verse “Has there not been over man a period of time, when he was not a thing worth mentioning?”
Question

                This has reference to chapter 76 Al-Insan or Ad Dahr verse 1. Has there not been over a man a period of time.... to be mentioned. What does the period of time imply? Is Adam peace be upon him Isaa peace be upon him and prophet (sws) are included in insan.
Praise be to Allah.Soorat al-Insaan begins 
    with a gentle rhetorical question which alerts man to the fact that he was 
    nothing before he was created, and Who is the one Who created him and made 
    him something worth mentioning after he had been nothing. It comes in the 
    form of a question so as to attract the listener’s attention and make him 
    listen out for the words that come after it. So Allaah says (interpretation 
    of the meaning):  
“Has there not been over 
    man a period of time, when he was not a thing worth mentioning?”
[al-Insaan 76:1]
The words insaan 
    (man) in this verse includes all of mankind, because all of mankind are 
    created; they came into existence after they did not exist and were not a 
    thing worth mentioning, as Allaah said to the Prophet Zakariya (peace be 
    upon him) (interpretation of the meaning): 
“He said: ‘So (it will 
    be). Your Lord says: It is easy for Me. Certainly I have created you before, 
    when you had been nothing!’”
[Maryam 19:9]. 
Shaykh ‘Abd al-Rahmaan 
    al-Sa’di (may Allaah have mercy on him) said: 
In this soorah Allaah 
    mentions the first state of man, and his beginning, middle and end. He says 
    that for a long time – which is before man was created – he was nothing, and 
    was not even worth mentioning. End quote. 
Tayseer al-Kareem 
    al-Rahmaan fi’l-Tafseer Kalaam al-Mannaan (p. 
    900). 
Al-‘Allaamah al-Taahir Ibn 
    ‘Ashoor (may Allaah have mercy on him) said: 
What this means is: Does 
    every man who exists realize that he was non-existent for a long time, and 
    he was not a thing worth mentioning, i.e., he had no name and he was not 
    spoken of. The word insaan (man) is used to refer to mankind in 
    general, as in the verse “Verily, man is in loss, Except those who 
    believe …” [al-‘Asr 104:2-3].
i.e., has there not been 
    over every man a period of time when he was not a thing? Dahr 
    (translated here as “a time”) refers to a long time. End quote. 
Al-Tahreer wa’l-Tanweer 
    (29/345-346). 
Perhaps this view, which 
    was narrated from Ibn ‘Abbaas and Ibn Jurayj, is more sound than the view 
    that it is Adam in particular who is referred to by the word insaan (man). 
    The context is general in meaning, and points to the general meaning of the 
    verse that comes after it, in which Allaah says (interpretation of the 
    meaning): “Verily, We have created man from Nutfah (drops) of mixed semen 
    (sexual discharge of man and woman), in order to try him, so We made him 
    hearer and seer” [al-Insaan 75:2]. It is known that it is the sons of 
    Adam who are created from “Nutfah (drops) of mixed semen”, so this 
    indicates that what is meant by the word insaan in the first verse is all of 
    mankind. 
This statement that man had 
    no prior existence has to do with the creation of man and reality.  In this 
    sense the statement includes all of mankind, even the Messengers and 
    Prophets. All of them were non-existent, then Allaah created them. 
With regard to the 
    knowledge of Allaah, all of mankind are known in Allaah’s eternal knowledge, 
    and are recorded in al-Lawh al-Mahfooz, but the Messengers and Prophets have 
    a special mention in the highest degrees, so they are the best of mankind, 
    and their being mentioned in the knowledge of Allaah is appropriate to the 
    high status of Prophethood and Messengership which Allaah has bestowed upon 
    them. 
And Allaah knows best.