Praise be to Allah.
The siraat is a bridge that will be set up over Hell – may Allah protect us from it – over which people will pass according to their deeds. Some will pass like the blink of an eye, or like lightning, or like the wind, or like swift horses.
Some will cross running, some walking, some crawling, and some will be snatched and thrown into the Fire, each according to his deeds.
In Saheeh al-Bukhaari (7439) and Muslim (183) it is narrated from Abu Sa‘eed al-Khudri (may Allah be pleased with him) in a lengthy hadith: “……Then the bridge will be laid across Hell.’ We said, "O Messenger of Allah! What is the bridge?’ He said, ‘It is a slippery (bridge) on which there are clamps and (hooks like) thorns which are wide at one side and narrow at the other and have bent ends. A plant with such thorns is found in Najd and is called al-Sa'daan. Some of the believers will cross the bridge as quickly as the wink of an eye, some others as quick as lightning, a strong wind, or fast horses or she-camels. So some will be safe without any harm; some will be safe after receiving some scratches, and some will fall down into Hell (Fire). The last person will cross by being dragged (over the bridge).”
Muslim added: Abu Sa‘eed said: I heard that the bridge is narrower than a hair and sharper than a sword.
The words “So some will be safe without any harm…” mean that they will fall into three categories: one category will be safe without experiencing any harm at all; another category will be scratched, then released and will be saved; and a third category will be snatched and thrown and will fall into Hell.
End quote from Sharh an-Nawawi ‘ala Muslim (3/29)
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
The siraat is a bridge that will be set up over Hell; it is narrower than a hair and sharper than a sword. People will pass over it according to their deeds. Whoever used to hasten to do good deeds in this world will pass quickly over the siraat; whoever was slow to do good deeds and whoever used to mix righteous deeds with bad deeds, and his bad deeds were not forgiven by Allah, may slip into the Fire; may Allah protect us.
People will vary in the ways in which they pass over the siraat. Some will pass in the blink of an eye, some will pass like lightning, some will pass like the wind, some will pass like swift horses, some will pass like fast camels, some will walk, some will crawl, and some will be thrown into Hell. No one will pass over this siraat except the believers only. As for the disbelievers, they will not pass over it, because on the Day of Resurrection they will be driven directly to Hell.
End quote from Sharh Riyaadh as-Saaliheen (1/470)
See also the answer to question no. 98714
This is a summary of what has been narrated concerning the passing of the people over the siraat, which will vary according to their deeds.
Whoever used to hasten in this world to obey and worship Allah will be quickest in passing over the siraat.
Whoever was slow (to obey and worship Allah) will pass over it slowly.
With regard to what is mentioned in the question about passing over it taking one thousand years to ascend and one thousand years to descend, we do not know of any basis for that. What one must do is stick to the texts and what they indicate.
And Allah knows best.