A while before Susa's death. Just before Lia and Leo escaped Timo.
The moment Lia put the grenade inside Timo's clothes, he instantly recognised it. It was one of the weapons in the headquarters. With this Timo figured out that Lia knew of the ghosts in the headquarters that Min was trying to breed and evolve.
As Lia jumped away from Timo, the latter quickly pulled the grenade out but not even a second later, it exploded in his hand. Half of his body was blown into bits. The fleshy outline of his figure barely stood its ground but Timo was unbothered by it.
After all, the grenades unlike the knives and swords were not infused with Min's life force, so they couldn't kill an immortal. Timo regenerated fast and when the smoke cleared, Lia and Leo had already left.