While Forti and its IPSEC is still in the works, I've posted short tutorial on how to get delayed hibernation working on every GNU/#Linux + SystemD based distro. https://sirmacik.net/delayed-hibernation-on-linux-with-systemd/?lang=en
@tadzik additionally:
~ % locate suspend.service
/etc/systemd/system/systemd-suspend.service
/usr/lib/systemd/system/systemd-suspend.service
/usr/share/man/man8/systemd-suspend.service.8.gz