This is supposed to be handled by the AccuracySec=, which is supposed to schedule timers at random times within the specified interval (in our case, 12h). I have no idea why this doesn't work, it's definitely worth looking into.
So far, I have seen all timers elapsing around midnight. But once I saw that, I quickly reverted to cron setup. One machine hasn't been updated yet, I will do it next week and perform more testing. But anyway, even if timers were spread between midnight and noon, this is hardly ideal either. Servers running maintenance tasks at unpredictable times, including work hours, is not really what I want to see. I can live with randomness or without it, but I would like more control over when things are happening, as had been possible with cron. I submitted request for enhancement to systemd bug tracker. The link is: https://bugs.freedesktop.org/show_bug.cgi?id=77938 However, now I started to worry about AccuracySec=12h. Even if systemd maintainers implement a way to customize timer elapse time (as I proposed in RFE), the long period in AccuracySec will then become a problem. Thanks Maciej Puzio