Yeah that time zone thing is tricky, I can feel the pain there... But looking your exporter, honestly it would be much greater with it
Maybe a master table for countries, codes and time zones... Then a lookup in spreadsheet if possible, at least when there is no info use the country time zone instead of GMT, something like that.
https://github.com/nabeelio/phpvms/pull/1481
Importer update PR is in, just waits big boss (Nabeel) to check and merge.
After all, your tool is nice (specially with that warnings and limitations per file) for beginners and people who have no access to official data. I still advise people to be careful though, not specific to your work but for all imports
Safe flights