Once the sun has risen from the west the door of repentance will be closed and will remain closed until the Day of Judgement. If any infidel embraces Islam or any Muslim repents and seeks forgiveness for his sins any time after the rising of the sun from the west till the Day of Judgement, it will not be accepted.
The Messenger of Allah(s.a.w.s) said, "Verily Allah extends his hand at night so that the sinners of the day may repent and verily extends his hand during the day so that the sinners of the night may repent. (He will keep on doing this) as long as the sun does not rise from the west." (Abu-Musa al-Ashari/ Muslim)
The Prophet(s.a.w.s) said, "Allah has built a door of repentance in the west the breadth of which is seventy years and it will not close as long as the sun does not rise from the west." (Safwan-b-Assal / Tirmidhi)
The above Ahadith have clearly specified that the extreme limit of the acceptance of repentance is till the sun rises from the west. Once it has risen it will not be accepted.
Ibne Hajar has mentioned many Ahadith which prove that the door of repentance will remain opened till the Day of Judgement and thereafter writes, ”These narration’s give strength to one another, agreeing completely in that when the sun rises from the west the door of repentance will be closed and will not be opened thereafter. And this is not specific with that day but will prolong till the Day of Judgement.” (Fathul- Bari)