Time zone setting as the alternative to the city time

[flyisland]

Right now there are two limitations of the city time:

1. You can not choose the city with less population.

Where multiple cities of the same name exist, currently, the one with the largest population will be chosen.

2. It depends on internet access which is not available always. For example sometimes after the plane takes off, I want to set the city to my destination. And the "google.com" is blocked in some places like China.

So I think we could have a "city time zone" setting, then we could calculate the gmtOffset independently.