time_zone_search.rb

# Search all zones for 8:00am.
(0..23).each do |hour|
  [0, 15, 30, 45].each do |minute|
    utc_time_to_check = Time.utc(2014, 6, 28, hour, minute, 0)
    TZInfo::Timezone.all_identifiers.each do |zone_name|
      local_tz = TZInfo::Timezone.get(zone_name)
      local_time = local_tz.utc_to_local(utc_time_to_check).to_datetime
      if local_time.minute == 0 && local_time.hour == 8 
        puts utc_time_to_check.strftime("%H:%M") + ' UTC => ' + local_time.strftime("%H:%M") + ' in ' + zone_name
      end
    end
  end
end

# Check non-zero minute offsets.
(0..23).each do |hour|
  [0, 15, 30, 45].each do |minute|
    utc_time_to_check = Time.utc(2014, 6, 28, hour, minute, 0)
    TZInfo::Timezone.all_identifiers.each do |zone_name|
      local_tz = TZInfo::Timezone.get(zone_name)
      local_time = local_tz.utc_to_local(utc_time_to_check).to_datetime
      if local_time.minute == 0 && local_time.hour == 8 && minute > 0
        puts utc_time_to_check.strftime("%H:%M") + ' UTC => ' + local_time.strftime("%H:%M") + ' in ' + zone_name
      end
    end
  end
end