xfce4-power-manager suspend to hibernate option?

I'd like to be able to suspend-then-hibernate automatically with xfce4-power-manager, though I'm not sure if this is possible.

I believe this is a permission error with polkit1 because:

$ xfce4-power-manager --dump
---------------------------------------------------
       Xfce power manager version 1.6.1
With policykit support
With network manager support
---------------------------------------------------
Can suspend: True
Can hibernate: False
Authorized to suspend: True
Authorized to hibernate: False
Authorized to shutdown: True
Has battery: True
Has brightness panel: True
Has power button: True
Has hibernate button: True
Has sleep button: True
Has LID: True

My polkitsettings under/usr/share/polkit-1/actions/org.freedesktop.login1.policyare identical for suspend and hibernate, so it doesn't make much sense whenxfce-power-manager` can't access hibernate options.

According to How to go automatically from Suspend into Hibernate?: I've created /etc/systemd/sleep.conf and tested it. The following command does work (suspend and then hibernates according to sleep.conf):

sudo systemctl suspend-then-hibernate

But this does not work when I use xfce4-power-manager to do the suspension.

A post I found (How to go automatically from Suspend into Hibernate?) is similar, but is not exactly what I'm trying to do. I don't care about lid closed operation, I want everything time related.