AD8602 Offset voltage variation


My customers are considering using the AD8602.
So I got a question.

They applied 2.0 V to the differential input pin and kept operating at 75 ° C for a long time.

(experimenting with the circuit below.
Connect a 6.8 kΩ resistor to GND and operate for several hours, then release GND and measure the offset voltage between Rload and R 4 with the following circuit.)

When the offset voltage was measured every few hours, the offset voltage decreased as time passed and it was lower by 50 uV in 100 hours than at the start of measurement.

# 1 Is this phenomenon due to NBTI?Or is there any other reason?

# 2 Is there graph data on offset voltage fluctuation measured along with voltage, temperature and time change?

Best Regards,