After deciding to create only three clones for now, Ling Tian devoted himself to cultivating the first clone's Primordial Spirit. Since the clone's Primordial Spirit directly received Primordial Spirit power from his main-body Nascent Soul, its cultivation advanced by leaps and bounds—several times faster than when he had cultivated his mental strength.
The main-body Nascent Soul only supplied Primordial Spirit power, so its cultivation level wouldn't drop. The depleted power was easy to replenish with the help of the heart and the soul power of the four golden cores. However, after supplying Primordial Spirit power, Ling Tian grew very tired and needed a period of rest to recover.
So, whenever his main-body Nascent Soul had recovered to its peak, Ling Tian transferred Primordial Spirit power to the clone's Primordial Spirit. Once he grew tired, he rested properly.
Even while resting, Ling Tian didn't sit idle. He continued multitasking, studying and practicing other things—alchemy, formations and restrictions, artifact refinement, and so on. Fortunately, his Mental Cultivation had already reached the Spirit Division Stage, so it could operate on its own even when he was exhausted. In fact, this circulation stimulated the main-body Nascent Soul's mental growth. He soon consolidated his Spirit Division Stage Mental Cultivation, and it even showed signs of slowly increasing.
Although he wasn't deliberately cultivating his heart, its cultivation continued to improve as Dan Star circulated on its own. It probably wouldn't be long before the heart reached the Spirit Division Stage, too.
However, cultivating the clone's Primordial Spirit to the Great Perfection of Divine Transformation Stage took much longer than the seven or eight months he'd expected. Even after a year had passed, it had only reached the Late Divine Transformation Stage. He had no idea how much longer it would take to reach the Great Perfection