systemd offers a timer able to replace cron. Here's a patch attempting to integrate this functionality into pgl and its build process. I've tested the resulting package against the latest stable release (2.2.4) successfully and hope everything will be up to pgl standards.
The mechanism is quite simple, consisting of 2 files: a service dedicated to the command "pglcmd update" and a timer calling the service at specific intervals.
The main pgl.service was updated to enable the timer at the same time that pgl.service is enabled. This replicates the defaults state of the cron script to make things simpler for users.
The rest of the diff is just makefile voodoo.