On the Arduino microcontroller, the millis() function counts the number of milliseconds since the program started running. Unfortunately, this count resets to zero after approximately 9 hours and 32 minutes. I have written a millisRollover() function that detects these rollovers, so that programs can respond properly to the overflow event. This can solve problems with servo routines, steppers, timed pauses and a variety of other calculations. In addition, because my millisRollover() function counts the number of times rollover has happened, it is now possible to record total Arduino runtime with a counter that’s good for over 35 years.
You want to blink an LED only on Christmas during leap years? Totally possible now.