Even with the arrival of the Fallen, the Horusians were still in the backfoot in the Legion Wars. The main reason for this was that, as long as the Crimson Accords forces had the initiative, the distorsion of time within the Eye of Terror mostly worked to the advantage of their enemies. Horus was on the defensive, sending reinforcements to strongholds that were under attack, and while the Cabalites had made communication faster and more reliable, actually moving the fleets through the unpredictable tides of the Eye of Terror was far more difficult. Some fleets arrived at their destination decades after the end of the siege, while others arrived days before the forces of the Crimson Accords entered the system – though the former was much more common. The Sorcerers of the Crimson Accords were using rituals to bend the time-twisting in their favor, and though these were costly and not entirely reliable, they were still a huge advantage for the Crimson Accords.
The Warmaster studied the Eye's very nature, puzzling out the eldritch ways in which the birth of the Youngest God had scarred reality and merged it with the Empyrean's madness. Within his chambers, Horus sought the means to end the temporal advantage of his enemies, using secrets that had been whispered in his heart by the Dark Gods themselves during the Heresy. He called Ahriman to him, and some of the greatest Horusian Sorcerers, as well as magi of the Dark Mechanicum and Techmarines who had embraced the power of Chaos – those who were now called Warpsmiths. All the while, his sons and allies fought on against the armies of Lorgar and Magnus, trusting that their Warmaster would deliver them victory.
And in the end, Horus succeeded. He emerged from his chambers and called the Warpsmiths to attend him, summoning them from all across his domain. Hundreds of artisans of Ruins answered Horus' call, and he explained his design to them. Under his direction, the Warpsmiths built a thousand and one great clocks at specific points on Maeleum, forming an arcane pattern of immense power. Each clock was a work of infernal greatness, forged from metal mined in the deepest mines of Maeleum, with every part crafted according to Horus' exacting specifications. But all of them were utterly silent, their machinery frozen until all preparations were complete.
The calculations were checked twelve times by a group of Ahriman and his Cabalites, and every clock was inspected for any flaw, no matter how minute. It took three months of replacing defective ones (and punishing those who had made them) before Horus was satisfied. Considering the scope of his ambition, anything less would have been beyond suicidal.
"You do realize that this is madness ?"
"Of course. But who, other than the mad, would dare triumph in Hell ?"
"… If I knew the answer, I would not be here, now would I ?"
Ahriman to Horus
With his Talon and his will, Horus cut through the Eye of Terror itself. He ripped apart the unreality of the Dark Prince's Grave-birth, and with his Gods-given powers, he reached through that opening and stole Time from the Materium, anchoring it through the greatest of the hell-forged clocks, a tower of black iron and brass over a kilometer tall, standing right above Horus' own throneroom. By this singular act, the Warmaster brought some of reality's order into the Realm of Chaos, as time now flowed on Maeleum in a constant, linear fashion – one hour passing on Maeleum now corresponded to one hour passing outside the Eye of Terror.
The flow of time passed through the thousand other clocks and through them and the dark arithmetics of the Warp, it was sent throughout the rest of the Horusian dominion. Entire daemon worlds were dragged into conformity to the laws of causality – kicking in screaming all the way, sometimes literally as the Chaos-bathed planets writhed under Time's touch. The further a daemon world was from Maeleum itself, the weaker the effect became, and even on Maeleum itself there remained locations too imbued with the energies of Chaos for the clocks to affect them.
Obalath tried to scream, but his body refused to answer to the orders coming from his brain. He would have panicked if only the necessary rush of oxygen and hormones could take place. The mutant's bestial face was wrinkling, ravaged by accelerated ageing as his mouth moved soundlessly, while the rest of his flesh remained unchanged. By the time his lungs finally responded to his injuction, his head had turned into dust.
In fact, the time-distorsions of these places grew worse after the building of the clocks, as if Chaos itself was compensating for what Horus had wrought. The Horusians soon learned to mark these places, where thousands of years could pass in the blink of an eye and from which crawled things spawned from the unfortunate who had been trapped within them upon Horus' grand gesture.
On Sicarius and Prospero, the Daemon Primarchs of the Crimson Accords felt the repercussions of Horus' titanic feat of sorcery. Lorgar was enraged, seeing what his brother had done as a gross violation of the Gods' holy realm. Magnus was silently impressed, and set many of his sons and servants to the task of uncovering how Horus had done this – if only so that they would know how to undo it once the Legion Wars were won without accidentally destroying the entire Eye.
Thanks to the Theft of Time, the logistics of the Legion Wars became much easier for the Horusians. The Warmaster could now wield all of his tactical genius, sending reinforcements toward strongholds that were exposed before the enemy could make his move and baiting and destroying entire fleets. Between the Cabalites' assistance, the Dark Angels recruits, and now this, the tide of the Legion Wars finally turned in the Horusians' favor.
For the first time since the Broken Conclave, the Sons of Horus and their Night Lord and Fallen allies were able to launch attacks on their own on the domains of the Crimson Accords. Temples of the Seventeenth Legion and observatories of the Fifteenth were razed, and those who had joined the alliance of Lorgar and Magnus were made to face the displeasure of the Warmaster.
In response, Lorgar dedicated more and more resources to the prosecution of the war. The Arch-Priest called upon the elder servants of Ruin, using the power granted unto him as a Daemon Primarch of Chaos Undivided. From the depths of the Gods' realms, the favored scions of Chaos emerged – a host of Daemon Princes, Greater Daemons, and other, less easily classified horrors. The Dark Gods were enjoying the Legion Wars immensely – even Horus' seeming disdain for the madness of the Eye was a source of great joy, for it had turned the course of the war on its head. The Ruinous Powers watched on, wondering what would be the next move of their favourite toy.
Did Lorgar and Magnus know what game their daemonic overlords were playing ? Possibly. For all that they were blind in so many ways, Aurelian and the Crimson King understood the Great Game of Chaos like few damned souls before them. But not even they could have anticipated Horus' next strike against the Accords.