All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu 'alyhi wa sallam, is His slave and Messenger.
The concept of intercession on behalf of those who committed grave major sins after being submitted to Hell is established through authentic Hadeeths.
As for the length of the period that they will spend in Hell as well as the longest period spent there, the knowledge of this is with our Lord in a record, and He neither errs nor forgets.
The bodies of the dwellers of Hell will not be able to bear the torture of the Fire. Rather, they will suffer severe pain until their skins will be roasted and they will be replaced with other skins. Describing the dwellers of Hell, Allaah The Exalted Says (what means): {Every time their skins are roasted through We will replace them with other skins so they may taste the punishment. Indeed, Allaah is ever Exalted in Might and Wise.} [Quran 4:56]
Out of the severe pain, they will say as Allaah The Exalted Says (what means) through their words: {And they will cry out therein, “Our Lord, remove us; we will do righteousness - other than what we were doing!”} [Quran 35:37]