I do not understand this procedure of retracting flaps on the landing roll as they will transistion from the gratest drag posistion to the greatest lift posistion on its way to a fully stowed posistion and adversely affect the weight on wheels for proper braking.
The objective on normal concrete or tarmac runways is to have the flaps stowed before turning onto a narrow taxiway where the engines may overhang the edges and foreign objects may be blown up, damaging the flaps. This is done late in the landing run at fairly low speed where any lift or drag considerations are minimal. Only a problem where taxiways are narrow and poorly laid out and more of a problem for turboprops than for jets.
Foreign object damage to flaps is a big problem at unmade airstrips where jets are unlikely to operate and pilots experienced in these conditions will have devoloped a habit of getting the flaps up as soon as reasonably practical to minimise the risk of damage.