You don't need the city longitude for Chinese astrology applications, unless your birth hour is around midnight or 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21 or 23 o'clock.
 

To find your city longitude, you need to type your birthplace name in the above link to find the city longitude. If the city longitude is 128w23, then use 128.23 as the west longitude in the Chinese calendar screen with a negative sign -128.23. If the city longitude is 118e36, then use 118.36 as the east longitude.

Chinese Lunar Calendar Conversion
Chinese Astrology Rise and Fall Chart
Daily Chinese Horoscopes