The titration of oxalic acid vs potassium permanganate in acidic medium is slow in the beginning but becomes fast after sometime... why ?

In titration of KMnO₄ and oxalic acid, KMnO₄ is an oxidizing agent and oxalic acid is a reducing agent.To initiate the reaction a little bit acid is required. So only dil.H₂SO₄ is used for these purpose. But the reaction is slower at acidic pH. As soon as reaction proceeds more and more Mn²⁺ is generate in solution. Mn²⁺ act as catalyst in this reaction. So as the concentration of Mn²⁺ increases, rate of reaction become faster with time. The redox reaction can be written as:
5H₂C₂O₄ + 2MnO₄^- + 6 H⁺ ----> 10CO2 + 2Mn²⁺ + 8H₂O