@keg, I’m not sure if you found your answer or not (I think I replied to something like your comment in a different thread, but I’m not sure if it’s worth moving it).
The snapd timer is internal; it won’t show up under
systemctl list-timers. That timer that you see, you can disable it if you want — it’s getting removed in an upcoming release after we confirmed it’s not needed (and confuses things for people wanting to set the refresh slower than that timer).
To see snapd’s timer, try
$ snap refresh --time timer: 00:00~24:00/4 last: 2018-03-07T23:35:00+01:00 next: 2018-03-08T05:09:00+01:00