Getting GCD to schedule and dispatch a packaged external task, like a backup, is actually straightforward. Here’s how.
Time Machine
An experimental tool to let you schedule background tasks of your own, which are managed by Grand Central Dispatch. First alpha release.
Irregular Time Machine backups are one of Sierra’s great mysteries. It now looks as if they might have been fixed in 10.12.4.
Schedule a periodic task as a Launch Agent. How close to the expected time does macOS actually run it?
Vastly improved over version 1, this now has over 6 MB of Help Book, with extensive reference material and links to online articles too.
Several significant improvements to CSV export to work around issues when importing to Excel and others.
Have you ever wished you could browse your logs in a spreadsheet, or analyse them using a statistics package? Now you can.
You can now save almost all your control settings as defaults. New windows then open with those settings ready for you. A great improvement.
This bug disrupts Time Machine backups and all the dozens of activities which macOS manages. It may make Sierra unsuitable for use in servers.
When Time Machine seems to take a long time preparing the next backup, or gets stuck, here is how to diagnose and deal with it.
The Eclectic Light Company 