Lex trained his body for half of a day, then absorbed the 2 clones that were cultivating and training, leaving the clone that was learning the Mental Void Method.
After absorbing and strengthening himself he reformed the two clones again and gave them the same instructions, but this time Lex cultivated his energy and after another half of a day reabsorbed the same two clones.
After suppressing and absorbing the energy and power from the clones, Lex had strengthened himself once again and could feel that he was nearing a limit that he would need to surpass.
After another half of a day, Lex completed the same cycle, however, this time felt as though he had reached his bottleneck of some sort and was unsure of what to do.
Conveniently the clone that was learning the Mental Void Method finished while he was contemplating on what to do to break past the bottleneck that he had reached.