The colloidal and aggregation behavior of asphaltenes in bulk dispersions is largely dependent on the solvent environment. Increasing the aliphatic fraction in these systems drives the aggregation of asphaltene clusters, leading to precipitation out of the bulk that can result in complications in the oil recovery and refining process. In this work, a millifluidic device is used to characterize the precipitation behavior of two asphaltene subfractions in good and poor solvent conditions to characterize the long-time solvency effects. Advantages to this approach are high discretization of the concentration gradient as well as shorter path lengths, which allow for better resolution of optical measurements in these extremely opaque systems. To measure precipitation, the critical aliphatic volume fraction (CAVF), defined in this work as the highest fraction of aliphatic solvent at which there is no visible precipitation in the sample, functions as a compositional breakpoint between stable and unstable dispersions. Results from this work show that asphaltene dispersions will reach a steady state after long times, on the order of months, of sample aging. Further, precipitation is visible at lower aliphatic fractions than what was determined in experiments using shorter aging times. This demonstrates how long-term effects should be considered when determining the stability of asphaltene dispersions.