Specifies the initial expiration of the timer. Setting either field to a non-zero value arms the timer. Setting both fields to zero disarms the timer.
Setting one or both fields to non-zero values specifies the period for repeated timer expirations after the initial expiration. If both fields are zero, the timer expires just once, at the time specified by it_value.
the previous expiration time as time().
Sets next expiration time of interval timer.