Is the game officially released for each region locally or is it all released at 00:01 GMT ? very confusing to work out when other countries can play the game on steam.

Locally for region - maybe +- 1 or 2 hours if your region is across many timezones. So americans get it at midnight their time (+-1 or 2 hours maybe), europeans get it at midnight their time, australians get it at midnight their time.

12:01 EST, for North America anyway.