Grayscale electron beam lithography (g-EBL) is a fabrication technique that allows for tunable control of resist topography. In most cases, the height of the structures is in the submicron regime. Here, we present an extensive experimental characterization of the post electron beam exposure behavior of poly(methyl methacrylate) (PMMA) 950 K for grayscale structuring with several micrometers in height. The obtained results show that the development depth for the same electron dose is dependent on the time between exposure and development. This dependence becomes more prominent at higher exposure doses. Additionally, it was found that a post-exposure bake influences the dose-response behavior of the resist material and, therefore, also the obtained three-dimensional (3D) structure. This work paves the way for well-controlled 3D micrometer structuring via g-EBL.