With JWST, new opportunities to study the formation and evolution of galaxies in the early Universe are now emerging. Spitzer constraints on rest-optical properties of π§ 7 galaxies demonstrated the power of using stellar masses and star formation histories (SFHs) of galaxies to indirectly infer the star formation history of the Universe. However, only the brightest individual objects at π§ 8 could be detected with Spitzer, making it difficult to robustly constrain past activity at π§ 10. Here, we leverage the greatly improved rest-optical sensitivity of JWST at π§ 8 to constrain the ages and SFHs of eleven UV-bright (π β19.5) galaxies selected to lie at π§ βΌ 8.5 β 11, then investigate implications for star formation activity at π§ 15. We infer the properties of individual objects in our sample with two spectral energy distribution modelling codes, then infer a distribution of ages for bright π§ βΌ 8.5 β 11 galaxies. We find a median age of βΌ 30 Myr, younger than that inferred at π§ βΌ 7 with a similar analysis, which is consistent with an evolution towards larger specific star formation rates at early times. The age distribution suggests that only βΌ 9 per cent of bright π§ βΌ 8.5 β 11 galaxies would be similarly luminous at π§ 15, implying that the number density of bright galaxies declines by approximately an order of magnitude between π§ βΌ 8.5 β 11 and π§ βΌ 15. This evolution is challenging to reconcile with some early JWST results suggesting that the abundance of bright galaxies does not significantly decrease towards very early times, but we suggest this tension may be eased if young stellar populations form on top of older stellar components, or if bright galaxies at π§ βΌ 15 are observed during a burst of star formation.