int warlock_t::imps_spawned_during( timespan_t period )
{
  int count = 0;

  for ( auto ev : wild_imp_spawns )
  {
    timespan_t ex = debug_cast<actions::imp_delay_event_t*>( ev )->expected_time();

    if ( ex < period )
      count++;
  }

  return count;
}