A 72-year-old woman with a history of hypertension and diabetes mellitus presents with acute onset of severe headache, vomiting, and left-sided weakness. CT head shows a 4 cm hyperdense lesion in the right basal ganglia with 8 mm midline shift and intraventricular extension. MRI performed 6 hours later shows the same lesion with T1 hyperintensity, T2 isointensity, and susceptibility artifact. What is the most likely timing of this hemorrhage, and what does the susceptibility artifact represent?