Built-in. The only thing you have to do is select what time it's closest to (increments of 3 hours), double click a button and it's off and running. You can customize the RGB channels to create 4 different programs, but I've not been that adventurous (read: lazy).
Have you looked at the Fluval 3.0 at all? That's the one that gets all the raves and has a better warranty than the Finnex. 3 years instead of whatever the Finnex has, which might sway you that way. There are definitely some bad reviews of the 24/7 out there, but mine has been without problems for the year and a quarter I've had it.
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