Dendrites are ubiquitous structures that are central to setting mechanical properties in materials, but the mechanism behind how dendrites grow is not fully understood. Using X-ray synchrotron radiation experiments, dendritic growth of Al-Cu alloys is studied in four-dimensions (three dimensions and time) to track the evolution of the three-dimensional structures as a function of time using novel X-ray tomography algorithms. Characterizing these large four-dimensional materials datasets is difficult due to the presence of complex microstructures and time-varying length scales. Two-point statistics algorithms are showcased as an efficient and un-biased way of extracting materials parameters from an Al-Cu alloy during solidification. The evolution of dendrite primary arm thickness, average secondary arm spacing, and average tip-to-tip spacing were tracked using two-point Pearson auto-correlations of scaled mean curvatures. These length scales have substantial influence on alloy hardness and tensile strength. Insights into competitive side-branching are also reported. We show both visually and quantitatively that most length scales change rapidly during early stages of dendritic growth, but slow as diffusion fields of dendrites overlap.