The death of Christ is envisaged as forming a pivotal point in history with God’s righteousness demonstrated there having effect for both the past and the future. kairos here denotes not just a moment in time or the passage of time, but time pregnant with significance—the appointed time, the time of opportunity, whose decisions and actions will determine the future.
James D. G. Dunn on Romans 3:26, Romans 1, WBC (1988), p. 174