According to Regina Buenaobra, ArenaNet’s North American Community Team Lead, the playable GW2 Living Story content starts on January 29th at around noon Pacific Time in Wayfarer Foothills and Diessa Plateau.
The playable Living Story content will start appearing tomorrow (January 29) at around noon Pacific Time in Wayfarer Foothills and Diessa Plateau. When the events start in Diessa Plateau, you’ll be sent an in-game mail letting you know about it. However, if you’re already logged in when that happens, you need to change maps to receive it.
Source: Forum GW2