From the wiki:
Monarchia, also known as the Perfect City was the capital city of the planet Khur. It was brought into compliance by the Word Bearers Legion 103 years prior to the events of Isstvan V.
It was utterly destroyed by the Ultramarines Legion six decades after being brought into compliance, as an example to both Lorgar and the Word Bearers demonstrating that their worship of the Emperor and the spread of such doctrine could not be tolerated. In the ashes of the city the entire XVII Legion gathered to be reprimanded by the Emperor, Roboute Guilliman and Malcador the Sigillite.1 Link
When the events described above were taking place, Emperor was still at the head of the Legions.
One of the crucial elements of the Fall of Horus was his wound, made by Nurgle sword, stolen by Lorgar from Interex and Erebus of World Bearers machination, which exposed Horus to the vision of the future. This means that Lograr has fallen before Horus.
So, to put everything in the timeline:
903.M30 The Word Bearers bring Forty-Seven Ten (Khur) to Compliance. They eventually turn the planetary capital Monarchia into a temple city dedicated to worship of the Emperor
964.M30 On the order of the Emperor of Mankind, the Ultramarines destroy Monarchia with seven days' notice. Lorgar and the Word Bearers arrive two months later and the Emperor forces them to kneel before him and Roboute Guilliman in the ashes of the Perfect City and its slain inhabitants. Only seven survivors are found, including Cyrene Valantion.
000.M31 The Ullanor Crusade comes to an end. The Emperor of Mankind and His armies destroy Ork warboss Urlakk Urg and the largest Ork empire in the galaxy. At the triumph celebrating the victory, the Emperor names Horus His Warmaster, renames the Luna Wolves the Sons of Horus, and retires to Terra.
004.M31 Erebus enters Horus' Warp vision disguised as Hastur Sejanus and tempts him with the powers of Chaos while Magnus the Red tries to dissuade him. Horus accepts the offer and awakens nine days after being interred in the Serpent Lodge's Delphos chamber. Magnus attempts to warn the Emperor of Horus' betrayal through forbidden sorcery, damaging the Golden Throne and psychic infrastructure on Terra in the process.
So the censure of Word Bearers has taken place 36 years before Horus became the Warmaster.