This study explored the temporal limits of cognitive change from an intention-to-treat with group music therapy. Elderly cognitively-impaired psychiatric inpatients (N = 28) participated in an 8-week randomized control trial using a crossover design. Once a week, subjects were assigned either to music therapy or a control treatment (age-appropriate movie). The Mini-Mental State Exam (MMSE) assessed cognition 3 times every week: prior to the intervention, immediately after the mid-afternoon intervention, and the morning following the intervention. Comparisons between conditions included weekly changes in individual subject's MMSE scores from weekly baseline to both the 2 follow-ups and the following week's baseline. Significant next morning improvements in MMSE scores were found within intent-to-treat music therapy cases as compared to control cases. While all the subjects in this study were cognitively impaired, only 17 had been formally diagnosed with dementia. Based on a Cochrane Collaboration suggestion that music therapy studies within geriatric populations look specifically at the treatment of dementia, a final generalized estimating equation model considered only the change within the 17 dementia-diagnosed subjects. Immediately after the intervention, MMSE scores in the dementia-diagnosed subjects assigned to music therapy improved 2.00 points compared to the dementia-diagnosed subjects assigned to the control group (Z = 1.99, p < .05). Next-day MMSE test scores in the dementia-diagnosed subjects assigned to music therapy showed average improvements of 3.69 points compared to the control subjects (Z = 3.38, p < .001). By the following week, no significant cognitive differences remained between the two groups. It was concluded that a reasonable music therapy intervention facilitated by a trained and accredited music therapist significantly improved next-morning cognitive functioning among dementia patients. With many music therapists working in geriatric settings, more research is justified to both replicate this study and provide better guidance into the effective use of music therapy in the treatment of dementia.