...

glBindVertexArray(VAO);
for(unsigned int i = 0; i < 10; i++)
{
    // calculate the model matrix for each object and pass it to shader before drawing
    glm::mat4 model;
    model = glm::translate(model, cubePositions[i]);
    float angle = 20.0f * i; 
    if(i % 3 == 0)  // every 3rd iteration (including the first) we set the angle using GLFW's time function.
        angle = glfwGetTime() * 25.0f;
    model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f));
    ourShader.setMat4("model", model);
    
    glDrawArrays(GL_TRIANGLES, 0, 36);           
}

...