When does Satan repent and recall the joys of heaven?

It is fair to say that Satan is decidedly unrepentant throughout Paradise Lost. However, he does at one point briefly consider whether or not he should repent for his disobedience. He quickly arrives at the conclusion, though, that even if he did, he wouold still have to bow down to God. That is not something he is prepared to consider.
Besides, Satan remains incredibly bitter at being cast down from Heaven, which he sees as his rightful abode. As far as he is concerned, he is the wronged party in all of this. Because he knows that there is no chance that he will ever be allowed to return, he plans to gets back at God by corrupting his creation. He is going to do this by getting Adam and Eve to eat from the Tree of Knowledge.
Satan, however, still recognizes the joys of heavenly life. If he did not, then there would be no cause for him to complain about being cast down. Satan puts a brave face on being expelled from Heaven, but there is no disguising his deep bitterness at what he regards as unjust treatment at the hands of the Almighty. There is no doubt that if he could, he would go back to Heaven in a heartbeat:

Farewell happy fieldsWhere Joy for ever dwells: hail horrors, hailInfernal world.

This is Satan trying to make the best of a bad situation. He acknowledges that joy will forever reign in Heaven, but he is still determined to make a new kingdom for himself, in which he alone will reign. That kingdom will be Hell, the "Infernal world."