Ordinary elixirs, as the name suggests, are for ordinary people's use, easy to make, while Human Elixirs are used by External Strength Warriors and are a bit more complex than ordinary elixirs.
Earth Elixirs, on the other hand, are for Internal Strength Warriors, the level of cultivation Ye Wudao is at now; making these is much more complex compared to Human Elixirs. Naturally, the elixirs that come after these are increasingly higher grade, harder to make, and increasingly tricky.
It was already eleven o'clock at night, and the elixir making was still not finished, over six hours had passed, and this was with Ye Wudao using a modernized alchemy room. Had it been the ancient method of using firewood for alchemy, it would have taken at least several days.