“For in six days the LORD made the heavens and the earth, the sea, and all that is in them, but he rested on the seventh day. Therefore the LORD blessed the Sabbath day and made it holy.” (Exodus 20:11)
As the six days account in Genesis 1 presents three days of creating environments – heaven (1st Day), sea and sky (2nd Day), finally land (3rd Day), and then three days returning to heaven (4th Day), sea and sky (5th Day) and land (6th Day) and populating those environments. Obviously this is not a scientific description of creation, as would be obvious also to the original Jewish scribes who recorded it, as morning and evening (1st Day) cannot occur without sun and moon (4th Day). Nevertheless within this presentation of creation in six days we are told that all that in heaven was made, so the angels would be in the six days somewhere.
Although some have suggest the 1st Day, it would be more consistent with the structure of the six days if angels as heavenly beings were assigned to the populating of the heavens on the 4th Day:
“And God made the two great lights—the greater light to rule the day and the lesser light to rule the night—and the stars” (Genesis 1:16)
But again, we don’t know, angels are not mentioned, only “sun, moon and stars” are mentioned. The word for stars (kokavim כּוֹכָבִֽים) here in Genesis 1:16 is the literal stars, not the “armies of heaven”, Sabbaoth, which is used later in the Bible both of stars and of the zodiac, and angels. For example both kokavim (stars) and sabbaoth (armies, host) are used together in Deuteronomy 4:19, so the two are connected.
A second related question to the above is Did angels help God create the earth or man? But the Bible contains no evidence of angels (the main meaning of which is simply ‘messengers’) helping create anything. The Genesis text only says that God (Elohim singular with singular verb ‘create’) made the world. No mention of angels doing anything except in later mentions, praising God.
he makes his messengers winds, his ministers a flaming fire. (Psalm 104:4)