anacron

I like anacron's ability to try and do a daily backup even if the machine
is never guaranteed to be up at any given time of day.

But I wish I could tell it to prefer some hours over others. So for
example, if the last backup took place at 2pm, it may still decide to do a
backup at 4am (when it doesn't bother me at all) so as to avoid doing the
next backup again at 2pm (when it can be disruptive).

Currently my only 2 options are to allow backup at "any time", or to
disallow backup at inconvenient times. I'd like something in between that
makes sure that backups are run at convenient times when possible, but are
also run at inconvenient times otherwise (because the potential disruption
is preferable to the risk of losing more data).