Is the duration of a day in Hellfire fifty or seventy thousand years, and is that specific to disbelievers, or does it include disobedient Muslims and those who are negligent in their prayers?

The state of disobedient people in the Fire is like that of others, and some of them will enter it for a period to be purified before entering Paradise. Allah the Almighty said concerning intentional murder: "And whoever kills a believer intentionally, his recompense is Hell, wherein he will abide eternally, and Allah has become angry with him and has cursed him and has prepared for him a great punishment." [Quran 4:93] It is also mentioned in the Hadith (definition) that a man may utter a word which he considers harmless, yet he falls with it into the Fire for seventy autumns. The dwellers of the Fire were asked: "What has caused you to enter Saqar? They will say: 'We were not of those who prayed, nor did we feed the poor, and we used to indulge in vain talk with those who indulged.'" [Quran 74:42-45] And whoever observes prayer, it will be a light, a proof, and a salvation for him on the Day of Resurrection. As for whoever does not observe it, he will be resurrected with Pharaoh, Haman, Qarun, and Ubayy ibn Khalaf. Intentionally abandoning an obligatory prayer is among the greatest sins.