Tempted to sudscribe to this for my DD. Silver package (the one where you get up to 12 books a month) seems best for her. Just wanted to know how long the 'swaps' take. Say I posted books back on a Monday a.m., when would I get my new books? Obviously need to send back books regularly to make hte most of swap allowance, but I don't want the books to spend most of the week with Royal Mail!