Some netball skirts are available as a stock line, whilst others are made to your order.  Netball Skirts available from stock are sent immediately, whilst made to order skirts can take 4-6 weeks to be ready to send, depending on the time of the year (during February to May allow the full six weeks).
Accurate sizing from the size charts depends on the accuracy of your measurements, so you might want to get a friend to help you with the tape measure.