You can reuse both disposable and washable masks (even before it is washed). It is recommended to change every 2-6 hours.
However, if your mask gets dirty, wet or damaged, or if you touch the inside of it, then you should change to a new one.
When you take it off to eat or drink, you should dispose of the old mask, wash or sanitise your hands, and replace it with a new one once you have finished eating.