Typically rapid palatal expansion is done with a jack screw that is activated at the rate of:: (A) 1.0 to 2.0 mm/week, (B) 1.0 to 2.0 mm/day, (C) 0.5 to 1.0 mm/week, (D) 0.5 to 1.0 mm/day
Answer is D. Every turn of the screw opens the appliance by 0.25 mm. 
Each turn involves 90° activation. 
With rapid maxillary expansion at a rate of 0.5–1 mm/day, a 10 mm expansion is achieved in 2–3 weeks.

Textbook of ORTHODONTICS Sridhar Premkumar