A numerical analysis is carried out using Atangana–Baleanu and Caputo–Fabrizio time‐fractional derivatives to study the mixed convective unsteady flow of a second‐grade fluid past an infinite vertical porous plate under the influence of a uniform transverse magnetic field. As finding the exact solutions of fluid equations presents huge difficulties due to the vagueness or uncertainty associated with the fluid parameters, fuzzy theoretic concepts are used rather than the classical crisp theoretic ones. Governing partial differential equations are made dimensionless and are then subject to fuzzification. The finite‐difference scheme is used to discretize the equations, and hence suitable programming codes are developed in PYTHON for AB and CF fractional derivatives. The results are obtained and plotted graphically. Interpretations based on these physical parameters imply that both AB and CF methods agreed well.