The words most often describing time duration in hell is "khalidina" or "khaliduna" and "abadan". These words do not necessarily mean "forever". There is no equivalent word in English that conveys these meanings. I think a more accurate meaning would be something like "very long time" or "unimaginably long time".
Due to this difference of opinion, it would not be logical to state that a certain Muslim sect definitively accepts a certain interpretation of eternity in hell. There will always be a difference of opinion. Ibn Taymiyyah, one of the most important early scholars of Sunni Islam, believed that hell was temporary. However, the current scholars of the Salafist sect, that has its foundations in Ibn Taymiyyah's teachings, and indeed most Sunni sects, differs on this view.
The question of eternity also rests on the assumption that time as we know it, or the passage thereof, will be similar in the "ahira" to as we know it in the "dunya". We cannot answer such a question going on an assumption.
That being said, and assuming that time in the ahira is similar to what we currently witness, the following similitude might help clarify.
We shall go by the premise Muslim belief that everyone is born Muslim, in a state of total submission to his/her creator and sustainer. Later, as a toddler, this state of total submission starts becoming corrupted by the other beliefs and indoctrination of his/her upbringing in a non-Muslim household. However, no matter how far this faith corruption goes in the course of his/her lifetime, there will always be that smidgen of faith in the one and only God, albeit deep within the heart and subconscious.
Since you only need a smidgen of faith to eventually get out of hell, then the logical conclusion is that hell can be a very long time, but in the end is temporary even for the most ardent denier.