We'd set up a derived collection of "timesheets that need approval" and export that to an emailer system. Every time a new entry shows up in that collection the

We'd set up a derived collection of "timesheets that need approval" and export that to an emailer system. Every time a new entry shows up in that collection the emailer will send out an email to the respective manager (whose email address would probably also be part of the data exposed to the emailer system). So, in essence, you hook up a separate system to a part of the data (we have a system ready made for this particular use case), and the datastore will push all changes in that data to this system.