3 week for safety purpose.. You can remove plaster after 2 week and apply crape bandage

Mason Type I radial head fractures are typically non-displaced and can often be managed conservatively. An above-elbow (A/E) slab is applied initially to reduce pain and allow the bone to start healing. Since you're currently experiencing no pain, that's a good sign of recovery. The usual duration for A/E slab use is 1 week, followed by gradual mobilization under guidance.

3 weeks is enough and can remove and start movements to prevent elbow stiffness if fracture is undisplaced