In Chapter Ten [of Canto Three] we get a very logical, evolutionarily sequential description of Creation progressing through 10 stages. Brahmā becomes involved from stage 7. In that 7th stage, Brahmā creates flora. In the 8th, fauna. In the 9th, humans. And in the 10th he creates super-humans.
In Chapter Twelve we seem to get other details. Basically, I can satisfactorily harmonize these details with Chapter Ten…
1. The five darknesses he creates are a refinement of darkness itself which evolved on its own prior to Brahmā’s birth (stage 6 of Chapter Ten).
2. Before creating the flora, fauna, humans and super-humans, he created some other important beings who are distinct from these four categories, namely: the Kumaras, the Rudras, the Prajapatis (Inc. Nārada and Kaśyapa), Vak/Sarasvatī, and finally Humans (Through Svāyambhuva Manu and Śatarūpā). The chapter describes other important things he created as well, that are not living beings.
So far so good, but then we get Chapter Twenty… describing Brahmā’s creation…
Text 18: He creates darkness
Text 19: He creates monsters/night
Text 22: He creates gods/day
Text 23: He creates demons/sunset
Text 38: He creates angels/moonlight
Text 40: He creates ghosts/sleep
Text 42: He creates Sādhya and Pitṛ/ Technology and Ritual
Text 44: He creates Siddhas and Vidyādharas / Magic
Text 45: He creates human-animal hybrids / sunrise
Text 47: He creates serpents and dragons / frustration and depression
Text 49: He creates humans (Manu) / the central life-form in the universe
Text 52: He creates the sages
To fit Chapters Twenty, Twelve, and Ten onto a single consistent timeline is challenging. But this seems to work: texts 19 through 47 give details about the 10th stage of creation (the super-human entities). Text 49 talks about the 9th stage (humans). Text 52 and 18 talk about things that happen after Brahmā’s birth but before stage 7 (flora).
To put it all into charts…
This is my conception of the first 6 stages of creation, taking all three chapter’s into account: