When did the creation of the first atomic nuclei, including hydrogen, occur?

In the seconds after the Big Bang during Big Bang Nucleosynthesis

The genesis of hydrogen nuclei is inextricably linked to the universe's earliest moments, a period characterized by extreme heat and density. As the universe expanded and cooled rapidly immediately following the Big Bang, conditions stabilized enough for fundamental particles to combine into the first stable nuclei—a process termed Big Bang Nucleosynthesis. This period was very brief, lasting only a few minutes. Due to the swift cooling and expansion, conditions were perfect only for forming the lightest nuclei, primarily single protons (hydrogen nuclei) and some helium nuclei, before the universe became too diffuse for further fusion reactions to occur efficiently.