There’s regional locks on it, which means basically that it needs to be midnight tonight in your region before you can play Mafia City.

 For the US, this is midnight eastern time. Take an hour off for each timezone you are west of there - nice and early 9pm start for the California/Seattle crowd.

 In the EU, it’s midnight British. That’s 1am if you’re on CEST, 2am if you’re a little further East.

Elsewhere, you’re best off checking the Steam page yourself. Just remember that Steam’s times are a little dodgy - if it says approx 10 hours, that’s 10 hours plus some amount of minutes. Gangster games, A midnight release will display as approximate two hours at 9:01pm because it is two hours and 59 minutes.