Duration: 9:30

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8 minutes timer, off more than 1 minute, the watchdog timer is very inaccurate, but it's actually as expected based on the datasheet, and the operational parameters.

1/f=t (time)
t=1/(128000/32768)=0.256s

with 3v VCC and 25, the actual watchdog frequency is about 112000
so, the actual timing is 1/(112000/32768)=0.292s

0.256/0.292=0.87
8 minutes/9 minutes=0.88
so the inaccuracy is actually very accurate.

PS. the 128 kHz watchdog can never reach that fast according to the datasheet. This is great if lower power is preferred, but very bad if accuracy is the issue.