One sentence, three relative clauses and a single conclusion. Ὧι … καὶ ᾧ … καὶ ᾧ … τούτῳ: three conditions converging on one dative. The construction matters: the fear of death is not refuted but set outside the brackets — we are told for whom it does not exist, and why.

The first condition sets the measure. τὸ εὔκαιρον μόνον TERMἀγαθόν — "the only good is the timely." Καιρός is "the due moment," and in 12.23 the question of death was settled by the same word: κατὰ καιρὸν παυσαμένη οὐδὲν κακὸν πάσχει. If the good is measured not by quantity but by fitness, the counting of years loses its point of itself.

The second and third are consequences of the first, and both concern number. "More right acts or fewer" — ἐν ἴσῳ ἐστί, "stands equal"; "to contemplate the world longer or shorter" — οὐ διαφέρει, "makes no difference." Both phrases are pointedly arithmetical: Marcus takes away from virtue and from life the one dimension in which death can take anything at all — length.

And the conclusion, stated without emphasis. τούτῳ οὐδὲ ὁ θάνατος φοβερόν — "to him not even death is fearful." Οὐδέ ("not even") places death last in an unseen series of things that have stopped frightening: first losses, then smallness, then at last death itself. Cf. 12.31, where the same result is got by cross-examining the wish to live, and 12.36, where it is got by the image of an actor dismissed from the stage. The governing discipline is desire, the sustaining one assent.