Did you try configuring a policy (like your default policy).
Click 'Configuration' on the top right, click 'Default Policy' (or the policy you're using right now). Go to 3a - check "Capacity Remaining is based on:" to "Usable Capacity", and then go to 3b, enable "% of Disk Space capacity to reserve as buffer" and set it to 20%. This should affect your remaining time... Check the provided screenshots. Let us know how that goes.
