MyBookLive-backup disappears if not accessed for several days

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.  



Are you able to change the settings on the Time Machine to see if you can make the software to update the backup on a daily basis or every two days.

Time Machine is setup to backup hourly but since I have two portable computers I only let it backup when they are connected to AC power.  Several days may pass before I have a chance to connect them to AC at home where my MBL is located.  Frequently, it is on the weekends when this typically happens.  More often than not when I have them at home and connected to power, they cannot find the MBL TM backup volume.  The MBL shows up but not the volume that is dedicated to TM backups.  It’s almost as if the TM backup volume times out if a backup hasn’t taken place for several days. The only way I have found to make the backup volume appear is to reboot the MBL.