Comment # 2 on bug 1206502 from Richard Brown

The reported behaviour is _exactly_ how we intend it to be

Users do not need every single update snapshot every single time, but need to
get it regularly

Even though the update is done in the background, it can have a performance
impact on CPU/Disk, so running it during/immediately after boot (where CPU/Disk
is always used heavily) can cause unwanted disruption from users.

So a randomised delay even with persistance is precisely the best balance of
ensuring users get their updates, and not being disruptive.