PRANAV,

IN PROBABILISTIC TERMS IT (TIMER/COUNTER OR ANY PERIPHERAL INSIDE A MICROCONTROLLER) DEPENDS ON ITS SILICON STRUCTURE/ CELL STRUCTURE AND VARIES FROM CHIP MAKER TO CHIP MAKER.

IF YOU ARE INTENDING TO USE THIS TIMER IN A VERY HI REL OPERATION LIKE SATELLITE OR REMOTE UNATTENDED APPLICATION THEN IT WILL BE SENSIBLE TO USE MIL GRADE PARTS AND THE MOST SIMPLE ONE AS LOWER THE TRANSISTOR COUNT INSIDE A CHIP MEANS A LOWER FAILURE PROBABILITY.

IN MY OWN EXPERIENCE ONCE WORKING AND IF AMBIENT CONDITIONS ARE NOT EXCEEDED THESE DEVICES SHALL WORK FOR A VERY REASONABLY LONG PERIODS LIKE TENS OF YEARS.

IT WILL BE STILL A NICE IDEA TO PUT SELF TEST INSIDE YOUR STARTUP RESET INIT PROGRAM AS WELL AS WDT KIND OF IMPLEMENTATION TO KEEP TRACK OF TIMER EVENTS.

HITESH