Workaround:
Create the following registry value in the following location to set this to a custom value:
HKLM\SOFTWARE\Wow6432Node\Quest\Recovery Manager for Active Directory\Options\
Name: MaxBackupsAgeInDays
Type: DWORD
Data: <decimal value>
For a 180 day tombstone lifetime, and if you want to see 180 day old backups, you would enter 180 in this location.
Restart the Recovery Manager for Active Directory Console and run the Online Restore wizard again.
Enhancement ID ADO-259764 has been submitted for consideration in a future release.
This will allow changing the days within the console interface.