In this study, oil-in-water emulsions stabilized with rice bran protein fibrils (RBPFs) were prepared, and the effect of the fibrils’ formation time on the structural and emulsion characteristics, including droplet size, zeta-potential, and surface morphology, were analyzed. As the heating time increased to 420 min, the β-sheet structure content and surface hydrophobicity of the RBPFs increased. As the heating time continued to heat up to 600 min, a downward trend occurred. The formation time also affected the mean contour length of the fibrils, and the scale began to decrease at 540 min. The emulsion prepared by heating for 480 min showed the best emulsifying activity, and the 420-min fibril emulsion showed the best emulsion stability and the highest interfacial protein content. The rheological results showed that as the heating time increased (0–480 min), the storage modulus increased, and the loss modulus and the apparent viscosity were reduced. The emulsions in the range of 0–100 s−1 shear rate did not have gel properties and shear thinning. The results of this study will help to provide a new perspective to develop a stable food-grade emulsion in the future.