If we are thinking of heaven in the sense of being in the presence of God, then heaven has always existed although it was only opened to human beings after Jesus’ Ascension into heaven (cf. CCC 661). If we are thinking of heaven in the sense of “the heavens,” then that happened at the beginning of time when God created “the heavens and the earth.” Genesis records that as having occurred on the first day of creation (cf. Gen. 1:1-5).
As for hell, because the “chief punishment of hell is eternal separation from God” (CCC 1035), hell was “created” as soon as a created being definitively and eternally chose against God. This means that hell began to exist when the fallen angels chose against God. Due to their purely spiritual nature, superior intelligence, and the “irrevocable character of their choice” (cf. CCC 393), the fallen angels could not repent and so cast themselves into hell.
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