One God the Father Translation/Commentary https://onegodtranslation.com/bible/2-peter/chapter-3/


Word Biblical Commentary, Jude-2 Peter, vol. 50, p. 338.
"on the day of eternity." This unique substitution for the phrase ("forever"), which is usual in doxologies, probably refers to the eschatological age as a day which will dawn at the Parousia (1:19) and last forever. The notion of the eternal day may derive from Isa 60:19-20:
"Your sun shall no more go down, nor your moon withdraw itself; for the Lord will be your everlasting light" (RSV; note the proximity to 60:22, echoed in 2 Pet 3:12).
The actual phrase ("the day of eternity") occurs elsewhere only in Sir 18:10: "Like a drop of water from the sea and a grain of sand so are a few years in the day of eternity" (Rsv).
Since that passage is based on Ps 90:4, it is possible that our author connected the phrase ("the day of eternity") with his reflection of Ps 90:4: the age to come is a day in the Lord's timescale which cannot be measured in the timescale of this world.
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