Got the time machine working with my 500 external drive. My understanding is backups will be performed hourly, then daily for a month and then weekly 'till the disk is full. So far I've used 200 gigs on this drive....at this rate the HD will be full in a couple weeks or so, meaning I won't have room for anything else on there. Is this correct? Is there away to reduce the frequency of these backups without just turning the time machine off manually?