vali.rb

  def has_conflict_of_times_in_activities?(schedule_activities)
    items = []

    schedule_activities.each do |schedule_activity|
      if has_time_intersection?(schedule_activity)
        items << schedule_activity
      end
    end
    items.any?
  end

  protected

  def has_time_intersection?(schedule_activity)
    (schedule_activity.time_range.include? start_time.to_s(:time)) || (schedule_activity.time_range.include? end_time.to_s(:time))
  end

  def time_range
    start_time.to_s(:time)..end_time.to_s(:time)
  end