@homer: Cron was written with an always-on server or a mostly-on desktop / laptop in mind.
A mobile device needs to actually be mostly-off to get the longest possible battery life, while appearing to the user to be on-demand-on.
The traditional tools for Linux simply we're not written with this use case in mind. So using them as is would degrade the use experience in an unacceptable way for most, if not all users.
That having been said, for as long as UT is still based on 16.04, you could use Upstart Session Jobs