Hello there now a days recommended duration of plaster cast is 28 days... so it means going by that rule you can remove the cast,however it is advisble to take an xray before the removal of cast so as to make sure that the fracture is healed completely....even after removal of your cast you have to consult a physio regarding how much weight you can put on the affected ankle and also the various ankle exercises (stability/balance/strengthning) to begin with. Take care Regards.