In this study, scoria lightweight aggregate concrete was produced with three aggregate gradation types (30–70, 40–60, and 20–40–40 including 20% natural sand) at a constant water-to-binder ratio of 0.42 and a cement content of 500 kg/m³, and was evaluated under three curing regimes: 24-h accelerated curing (X), 28-day curing, and 90-day curing. The study provides a coupled assessment of gradation type, metakaolin replacement level, and curing regime in terms of compressive strength, dynamic modulus of elasticity, water absorption, and water penetration depth. Mix CM15[90D] achieved the highest compressive strength (40 MPa), whereas CM15[X] reached 32 MPa (20% lower than the maximum). Owing to the porous nature of scoria aggregates, the dynamic modulus varied within a relatively narrow range across mixtures. CM15[X] exhibited the lowest water absorption, and CM15[90D] was only 5.5% higher than this minimum. The minimum water penetration depth was recorded for CM15[90D] (30 mm), corresponding to a 25% reduction relative to the age-matched control; the same mixture under X curing showed a 14.75% reduction. Moreover, the inverse relationship between compressive strength and water penetration depth was most consistent for gradation type C (R² = 0.9706). Overall, the combined use of metakaolin and accelerated curing enables rapid screening of mix designs within 24 h while improving durability-related indicators.