The Experiment for X-ray Characterization and Timing (EXACT) mission will be a CubeSat based, hard X-ray spectrometer for measuring high-energy emission from solar flares with high time precision. Solar flares and the related coronal mass ejections affect space weather and the near-Earth environment through emission of solar energetic particles. Hard X-rays (HXRs) are emitted from flare-Accelerated electrons, which are energized at or near the time of energy release, and therefore serve to probe the timing of energy release and particle acceleration. EXACT will study the hard X-rays generated by the Sun in the declining phase of Solar Cycle 24 in order to probe electron acceleration in flares and solar eruptive events while also serving as a precursor to future hard X-ray spectrometers that could monitor the Sun continuously. EXACT's secondary mission is to demonstrate a spacecraft ranging technique based on timing of astrophysical X-ray and gamma ray bursts. EXACT will be a 3U (10x10x30 cm3) CubeSat. This paper will discuss the scintillator detector under development for the mission, including the modeling of the detector response function, as well as expected observations of solar flares by EXACT.