after five months the clock is early 30 minutes

[mackrackit]

From the data sheet...

CLOCK ACCURACY
The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match between
the capacitive load of the oscillator circuit and the capacitive load for which the crystal was trimmed. Additional
error will be added by crystal frequency drift caused by temperature shifts. External circuit noise coupled into the
oscillator circuit may result in the clock running fast. Refer to Application Note 58: Crystal Considerations with
Dallas Real-Time Clocks for detailed information.

[mister_e]

well, assuming it's on a PCB, you could do some software trick like correcting the seconds, or minute each day or every months to compensate it... probably another silly idea though