After:
APP_TIMER_INIT(APP_TIMER_PRESCALER, APP_TIMER_MAX_TIMERS, APP_TIMER_OP_QUEUE_SIZE, true);
and:
app_timer_create(&m_sysctl_timer_id, APP_TIMER_MODE_REPEATED, sysctl_timer_event);
app_timer_start(m_sysctl_timer_id, ticks, NULL);
Will sysctl_timer_event() execute under control of app_sched_execute() at MAIN user context level?