For some of my clients, sometimes I am setting up quite a few new PCs at the same time. Thanks to Microsoft all are in Pacific Time Zone.

For Windows 7 and up, there is tzutil tool. This tool allows you to set timezone quickly:

tzutil /s "Eastern Standard Time"

You can see the current zone via /g parameter and you can see list of available zone names via /l

tzutil /l
(UTC-12:00) International Date Line West
Dateline Standard Time

(UTC-11:00) Coordinated Universal Time-11
UTC-11

(UTC-10:00) Aleutian Islands
Aleutian Standard Time

(UTC-10:00) Hawaii
Hawaiian Standard Time

(UTC-09:30) Marquesas Islands
Marquesas Standard Time

(UTC-09:00) Alaska
Alaskan Standard Time

(UTC-09:00) Coordinated Universal Time-09
UTC-09

(UTC-08:00) Baja California
Pacific Standard Time (Mexico)

(UTC-08:00) Coordinated Universal Time-08
UTC-08

(UTC-08:00) Pacific Time (US & Canada)
Pacific Standard Time

(UTC-07:00) Arizona
US Mountain Standard Time

(UTC-07:00) Chihuahua, La Paz, Mazatlan
Mountain Standard Time (Mexico)

(UTC-07:00) Mountain Time (US & Canada)
Mountain Standard Time

(UTC-07:00) Yukon
Yukon Standard Time

(UTC-06:00) Central America
Central America Standard Time

(UTC-06:00) Central Time (US & Canada)
Central Standard Time

(UTC-06:00) Easter Island
Easter Island Standard Time

(UTC-06:00) Guadalajara, Mexico City, Monterrey
Central Standard Time (Mexico)

(UTC-06:00) Saskatchewan
Canada Central Standard Time

(UTC-05:00) Bogota, Lima, Quito, Rio Branco
SA Pacific Standard Time

(UTC-05:00) Chetumal
Eastern Standard Time (Mexico)

(UTC-05:00) Eastern Time (US & Canada)
Eastern Standard Time

(UTC-05:00) Haiti
Haiti Standard Time

(UTC-05:00) Havana
Cuba Standard Time

(UTC-05:00) Indiana (East)
US Eastern Standard Time

(UTC-05:00) Turks and Caicos
Turks And Caicos Standard Time

(UTC-04:00) Asuncion
Paraguay Standard Time

(UTC-04:00) Atlantic Time (Canada)
Atlantic Standard Time

(UTC-04:00) Caracas
Venezuela Standard Time

(UTC-04:00) Cuiaba
Central Brazilian Standard Time

(UTC-04:00) Georgetown, La Paz, Manaus, San Juan
SA Western Standard Time

(UTC-04:00) Santiago
Pacific SA Standard Time

(UTC-03:30) Newfoundland
Newfoundland Standard Time

(UTC-03:00) Araguaina
Tocantins Standard Time

(UTC-03:00) Brasilia
E. South America Standard Time

(UTC-03:00) Cayenne, Fortaleza
SA Eastern Standard Time

(UTC-03:00) City of Buenos Aires
Argentina Standard Time

(UTC-03:00) Greenland
Greenland Standard Time

(UTC-03:00) Montevideo
Montevideo Standard Time

(UTC-03:00) Punta Arenas
Magallanes Standard Time

(UTC-03:00) Saint Pierre and Miquelon
Saint Pierre Standard Time

(UTC-03:00) Salvador
Bahia Standard Time

(UTC-02:00) Coordinated Universal Time-02
UTC-02

(UTC-01:00) Azores
Azores Standard Time

(UTC-01:00) Cabo Verde Is.
Cape Verde Standard Time

(UTC) Coordinated Universal Time
UTC

(UTC+00:00) Dublin, Edinburgh, Lisbon, London
GMT Standard Time

(UTC+00:00) Monrovia, Reykjavik
Greenwich Standard Time

(UTC+00:00) Sao Tome
Sao Tome Standard Time

(UTC+01:00) Casablanca
Morocco Standard Time

(UTC+01:00) Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna
W. Europe Standard Time

(UTC+01:00) Belgrade, Bratislava, Budapest, Ljubljana, Prague
Central Europe Standard Time

(UTC+01:00) Brussels, Copenhagen, Madrid, Paris
Romance Standard Time

(UTC+01:00) Sarajevo, Skopje, Warsaw, Zagreb
Central European Standard Time

(UTC+01:00) West Central Africa
W. Central Africa Standard Time

(UTC+02:00) Amman
Jordan Standard Time

(UTC+02:00) Athens, Bucharest
GTB Standard Time

(UTC+02:00) Beirut
Middle East Standard Time

(UTC+02:00) Cairo
Egypt Standard Time

(UTC+02:00) Chisinau
E. Europe Standard Time

(UTC+02:00) Damascus
Syria Standard Time

(UTC+02:00) Gaza, Hebron
West Bank Standard Time

(UTC+02:00) Harare, Pretoria
South Africa Standard Time

(UTC+02:00) Helsinki, Kyiv, Riga, Sofia, Tallinn, Vilnius
FLE Standard Time

(UTC+02:00) Jerusalem
Israel Standard Time

(UTC+02:00) Juba
South Sudan Standard Time

(UTC+02:00) Kaliningrad
Kaliningrad Standard Time

(UTC+02:00) Khartoum
Sudan Standard Time

(UTC+02:00) Tripoli
Libya Standard Time

(UTC+02:00) Windhoek
Namibia Standard Time

(UTC+03:00) Baghdad
Arabic Standard Time

(UTC+03:00) Istanbul
Turkey Standard Time

(UTC+03:00) Kuwait, Riyadh
Arab Standard Time

(UTC+03:00) Minsk
Belarus Standard Time

(UTC+03:00) Moscow, St. Petersburg
Russian Standard Time

(UTC+03:00) Nairobi
E. Africa Standard Time

(UTC+03:00) Volgograd
Volgograd Standard Time

(UTC+03:30) Tehran
Iran Standard Time

(UTC+04:00) Abu Dhabi, Muscat
Arabian Standard Time

(UTC+04:00) Astrakhan, Ulyanovsk
Astrakhan Standard Time

(UTC+04:00) Baku
Azerbaijan Standard Time

(UTC+04:00) Izhevsk, Samara
Russia Time Zone 3

(UTC+04:00) Port Louis
Mauritius Standard Time

(UTC+04:00) Saratov
Saratov Standard Time

(UTC+04:00) Tbilisi
Georgian Standard Time

(UTC+04:00) Yerevan
Caucasus Standard Time

(UTC+04:30) Kabul
Afghanistan Standard Time

(UTC+05:00) Ashgabat, Tashkent
West Asia Standard Time

(UTC+05:00) Ekaterinburg
Ekaterinburg Standard Time

(UTC+05:00) Islamabad, Karachi
Pakistan Standard Time

(UTC+05:00) Qyzylorda
Qyzylorda Standard Time

(UTC+05:30) Chennai, Kolkata, Mumbai, New Delhi
India Standard Time

(UTC+05:30) Sri Jayawardenepura
Sri Lanka Standard Time

(UTC+05:45) Kathmandu
Nepal Standard Time

(UTC+06:00) Astana
Central Asia Standard Time

(UTC+06:00) Dhaka
Bangladesh Standard Time

(UTC+06:00) Omsk
Omsk Standard Time

(UTC+06:30) Yangon (Rangoon)
Myanmar Standard Time

(UTC+07:00) Bangkok, Hanoi, Jakarta
SE Asia Standard Time

(UTC+07:00) Barnaul, Gorno-Altaysk
Altai Standard Time

(UTC+07:00) Hovd
W. Mongolia Standard Time

(UTC+07:00) Krasnoyarsk
North Asia Standard Time

(UTC+07:00) Novosibirsk
N. Central Asia Standard Time

(UTC+07:00) Tomsk
Tomsk Standard Time

(UTC+08:00) Beijing, Chongqing, Hong Kong, Urumqi
China Standard Time

(UTC+08:00) Irkutsk
North Asia East Standard Time

(UTC+08:00) Kuala Lumpur, Singapore
Singapore Standard Time

(UTC+08:00) Perth
W. Australia Standard Time

(UTC+08:00) Taipei
Taipei Standard Time

(UTC+08:00) Ulaanbaatar
Ulaanbaatar Standard Time

(UTC+08:45) Eucla
Aus Central W. Standard Time

(UTC+09:00) Chita
Transbaikal Standard Time

(UTC+09:00) Osaka, Sapporo, Tokyo
Tokyo Standard Time

(UTC+09:00) Pyongyang
North Korea Standard Time

(UTC+09:00) Seoul
Korea Standard Time

(UTC+09:00) Yakutsk
Yakutsk Standard Time

(UTC+09:30) Adelaide
Cen. Australia Standard Time

(UTC+09:30) Darwin
AUS Central Standard Time

(UTC+10:00) Brisbane
E. Australia Standard Time

(UTC+10:00) Canberra, Melbourne, Sydney
AUS Eastern Standard Time

(UTC+10:00) Guam, Port Moresby
West Pacific Standard Time

(UTC+10:00) Hobart
Tasmania Standard Time

(UTC+10:00) Vladivostok
Vladivostok Standard Time

(UTC+10:30) Lord Howe Island
Lord Howe Standard Time

(UTC+11:00) Bougainville Island
Bougainville Standard Time

(UTC+11:00) Chokurdakh
Russia Time Zone 10

(UTC+11:00) Magadan
Magadan Standard Time

(UTC+11:00) Norfolk Island
Norfolk Standard Time

(UTC+11:00) Sakhalin
Sakhalin Standard Time

(UTC+11:00) Solomon Is., New Caledonia
Central Pacific Standard Time

(UTC+12:00) Anadyr, Petropavlovsk-Kamchatsky
Russia Time Zone 11

(UTC+12:00) Auckland, Wellington
New Zealand Standard Time

(UTC+12:00) Coordinated Universal Time+12
UTC+12

(UTC+12:00) Fiji
Fiji Standard Time

(UTC+12:45) Chatham Islands
Chatham Islands Standard Time

(UTC+13:00) Coordinated Universal Time+13
UTC+13

(UTC+13:00) Nuku'alofa
Tonga Standard Time

(UTC+13:00) Samoa
Samoa Standard Time

(UTC+14:00) Kiritimati Island
Line Islands Standard Time