I've encountered an expression which uses a Landau symbol (big O) within an expression. I'm only familiar with this syntax for expressing functional complexity. I'm wondering how this might be interpreted and evaluated. I encountered this expression when deriving a degree distribution for a Bianconi-Barabasi network model (Eq 6.36, Source). I've been unable to find info on this usage, other than it represents a substitution under certain (asymptotic) conditions.
$$⟨∑_jη_jk_j⟩=^{t→∞}Cmt(1−O(t^{−ε}))$$ $$ε = (1 − \mbox{max}_ηβ(η)) > 0$$