The Glymphatic system model describes how cerebral spinal fluid (CSF) bulk movement in and around the brain is mediated by changes in cerebral hemodynamics, thereby removing waste products. Physiological factors such as the sleep-wake cycle could influence its function. This system could play a decisive role in the pathology of neurodegenerative diseases, hence its relevance for investigation. Novel fMRI tools, e.g., the correlation between global grey matter (gGM) BOLD and CSF flow signal, have enabled neuroimaging researchers to study the system’s function. Yet, no studies are looking at whether the time of fMRI acquisition might influence results. We used resting-state fMRI recordings from healthy young adults from the Human Connectome Project S1200 dataset. To simplify, data were categorized into three groups (9-11a.m., 1:30-3:30p.m., and 6-8p.m.) depending on the time of the day of acquisition. We correlated the negative derivative of the mean signal of all grey matter cortical voxels in the brain with the CSF flow signal at the bottom slice of the image as a proxy of glymphatic system function. A one-way ANOVA was performed to examine the group’s influence on the resulting coupling value. Preliminary results using 54 subjects show that the group (i.e., time of the day) is not related with variations in the coupling values [F(2,51) = 0.80, p = 0.46], yet a bigger sample size is needed to be tested. This is critical to know, e.g., in the context of the validity of clinical studies, which might be done on different day times.