When was the start of Heartless

If you know KH2, then you probably saw a man named DiZ with red bandages on his head and face. He is the start. He had about seven apprentices, and one day they took his research into the depths of the heart too far. They conducted experiments he didn't permit, and soon they became so powerful with the heart their original forms vanished and they became Heartless. The only human form of Heartless we know of is DiZ (originally Ansem the Wise)'s closest apprentice Xehanort, who was the renagading apprentices' leader. This Heartless stole Ansem the Wise's name and used it for evil, banishing DiZ into oblivion and nothingness. Long story short, the Heartless began with an experiment gone too far.

IN the night i hear them talk the coldest story ever told somewhere far along this road he lost his soul to a woman so heartless.....oh how can you be so heartless?.....