I have a 2TB MBL that I use to back up two MacBooks using Time Machine. Often several days may elapse before I want to allow backups to happen. I have noticed that on both Macs that if I have not backed up for several days the -backup volume is not listed under Shared in Finder. The MBL still shows up under Shared but not the TM backup volume. The only way I can get this to reappear is to reboot the MBL. At latest version of firmware on the MBL and router.