When inserting the batteries in the 'Home' radon detector, it will take around 24 hours until you receive the first measurement. It is typical with higher radon levels you will get your first indication measurement in a shorter time.
Keep in mind this is just your first indication and we recommend measuring for at least one month to begin to really understand your radon levels and understand if action is needed, check out our article here: How to respond to your radon levels