ʿUthman ؓ was killed in 35 AH and the fitnah (turmoil) lasted for five years including four months of al-Hasanʿs rule.
عَنْ عَبْدِ اللهِ بْنِ مُحَمَّدِ بْنِ عَقِيلٍ قَالَقُتِلَ عُثْمَانُ سَنَةَ خَمْسٍ وَثَلاثِينَ فَكَانَتِ الْفِتْنَةُ خَمْسَ سِنِينَ مِنْهَا أَرْبَعَةُ أَشْهُرٍ لِلْحَسَنِ