All dates and times in Promo are stored in Coordinated Universal Time (UTC). Further to this, dates and times that are submitted in Promo API requests, and those returned in responses from Promo API requests will always be in UTC.
In the Promo Portal all dates and times are presented based on the local timezone. The timezone used can be adjusted from the Timezone Selector towards the top right of the Portal page, next to the User menu, with quick links to jump between Local and UTC.
The setting Format for displaying date is used to define how dates will be presented in the Promo Portal.