If I start a number of process that could represent clients that is running in different TimeZones I can (depending on the actual code) use the TZ enivroment to make them look like they come from different timezones.
Is there a more proper windows way to simulate this, without starting 24 virtual machines?
Different processes in Windows can certainly run with different environments. If your process uses the TZ environment variable to determine its time zone, then you can just set that environment variable individually before launching each process.
The C runtime library (eg. localtime) uses the TZ environment variable, but the Win32 API (eg. GetLocalTime) does not. So, depending on how your application determines the local time zone, this technique may or may not work for you.