Standalone ATmega clock continuous lifetime Here I have made a standalone ATmega328p clock without
any RTC module using the breadboard ATmega328p , LCD I2C , and some buttons which I would like to turn on for atleast an year (supposed to be without any reset or power-interrupts).
I am powering my ATmega using an old mobile charger (5v , 500mA) of a old broken Android.
However I am not using any millis() or something alike these in the clock code,
So how long will my clock run if is it supposed to be online 24/7
Should I reset it sometimes?
If yes , when, after how many days should I reset it?
And do I need a coolant system for it? (I guess not)
Thanks for your precious time .
So how long will my clock run if is it supposed to be online 24/7

Until you turn it off or a stray neutrino corrupts the flash memory, or the flash memory degrades (20-100 years or so depending on temperature).

Should I reset it sometimes? If yes , when, after how many days should I reset it?

No.

And do I need a coolant system for it? (I guess not)

No. Not unless it's in a sealed container with no ventilation and a hot environment.
However
Your RTC-less &quot;clock&quot; will probably not be particularly accurate, unless you have some external source of time (NTP, GPS, etc) as the Arduino's internal timing is not very accurate, and built on a breadboard it's even less so due to excess stray capacitance.