Job tells of the time when the universe was created, and the angels sang and praised his work:
Tell me, since thou art so wise, was it thou or I designed earth’s
plan, measuring it out with the line? How came its base to stand so
firm; who laid its corner-stone? To me, that day, all the morning
stars sang together, all the powers of heaven uttered their joyful
praise. -- New Advent -- Job 38:5-7
These spirit beings (stars are symbolic of angels) obviously preceded the creation of mankind.
The Catholic Encyclopedia contains a long article about the Devil, giving great detail about Satan and his fallen angels. In particular:
... the words of St. Jude: "And the angels who kept not their
principality, but forsook their own habitation, he hath reserved under
darkness in everlasting chains, unto the judgment of the great day"
(Jude 1:6; cf. 2 Peter 2:4).
In the Old Testament we have a brief reference to the Fall in Job
4:18: "In his angels he found wickedness". But to this must be added
the two classic texts in the prophets:
How art thou fallen from heaven, O Lucifer, who didst rise in the
morning? how art thou fallen to the earth, that didst wound the
nations? And thou saidst in thy heart: I will ascend into heaven, I
will exalt my throne above the stars of God, I will sit in the
mountain of the covenant, in the sides of the north. I will ascend
above the height of the clouds, I will be like the most High. But yet
thou shalt be brought down to hell, into the depth of the pit. (Isaiah
This parable of the prophet is expressly directed against the King of
Babylon, but both the early Fathers and later Catholic commentators
agree in understanding it as applying with deeper significance to the
fall of the rebel angel. And the older commentators generally consider
that this interpretation is confirmed by the words of Our Lord to his
disciples: "I saw Satan like lightning falling from heaven" (Luke
10:18). For these words were regarded as a rebuke to the disciples,
who were thus warned of the danger of pride by being reminded of the
fall of Lucifer.
The parallel prophetic passage is Ezekiel's lamentation upon the king
You were the seal of resemblance, full of wisdom, and perfect in
beauty. You were in the pleasures of the paradise of God; every
precious stone was thy covering; the sardius, the topaz, and the
jasper, the chrysolite, and the onyx, and the beryl, the sapphire, and
the carbuncle, and the emerald; gold the work of your beauty: and your
pipes were prepared in the day that you were created. You a cherub
stretched out, and protecting, and I set you in the holy mountain of
God, you have walked in the midst of the stones of fire. You were
perfect in your wave from the day of creation, until iniquity was
found in you. (Ezekiel 28:12-15)
The spiritual creation and later Lucifer's rebellion and fall obviously occurred before the seven days of creation.
... it is clearly taught that the Devil and the other demons are
spiritual or angelic creatures created by God in a state of innocence,
and that they became evil by their own act.