how much time is needed to charge airpods pro case?

how much time is needed to charge AirPods pro case? Actually I recently bought my first set of AirPods Pro so I don't have much knowledge how much time is sufficient for charging the case. I tried charging it for half an hour for the first time and then for an hour, but the case still won't reach 100% battery capacity. so how much time is sufficient for completely charging the case?