You can configure how long each kind of break lasts, and how long between breaks, or disable each kind. Each Time Out is announced via the screen slowly dimming, with related graphics materializing, and when the break is complete, it fades out again. You can change the time these transitions take and you can even change the color and the level of transparency during the break. So if you like, you can make it mostly transparent so you can continue reading while on your break... though it's better for you if you give your eyes a rest during the Time Out. At the start and/or end of the break, you can optionally play a sound, and even run an Automator workflow, AppleScript, or application.
Time Out is released as Freeware. You are welcome to use it at no cost.
What's new in this version:
A few people had difficulty with the idle detection, so this version attempts to address that. If the idle interval returned by the OS seems invalid, it tries a similar but different approach to get a more sensible value.