We report on the quantitative determination of the transient surface temperature of Pt(110) upon nanosecond laser pulse heating. We find excellent agreement between heat transport theory and the experimentally determined transient surface temperature as obtained from time-resolved X-ray diffraction on timescales from hundred nanoseconds to milliseconds. Exact knowledge of the surface temperature's temporal evolution after laser excitation is crucial for future pump-probe experiments at synchrotron storage rings and X-ray free electron lasers. Published by AIP Publishing.