There's actually an easy way to do that by simply having a daemon that does whatever it needs at the appropriate time. Should be easy to do that reusing existing tools that perform this task instead of writing something new.
That said, we definitely want to support timer units to be configured directly in snap.yaml and then snapcraft.yaml.
Should be pretty simple to introduce the feature from where we are. We just need to agree on how to specify these settings and then map it into the underlying system. Good topic for the sprint next week.