in short …so far I learned that :
- in deep sleep (power off) You can not wake up the device using timer .
- in power on sleep ( sd_app_evt_wait() ) You can use timers to wake up the device
… The only way to wake up the nRF is with one of a few specific external wakeup signals (GPIO, LPCOMP, NFC or pin reset). A wakeup from system off is always in form of a reset…