Hi Yossi,
Here is the case,
If you use activity interrupt, when there is one sample over the 12g threshold, the activity interrupt will be triggered, it cannot wait for 300 ms.
If you use single_tap interrupt, when the acceleration over 12g and last for 300 ms, the single_tap interrupt cannot be triggered unless the next sample is less than 12g.
I would suggest you to check ADXL362, its activity interrupt supports more samples trigger function. This means you can specify how many samples (or say how long time) over the threshold, then trigger the activity interrupt.
Please check page 27 of ADXL362 datasheet for more details.
BR
Neil
