From the page Nikel referenced:
Both localized and non-localized attributes are stored in UTC but only localized attributes are shown in the time zone of the user when displaying (or picking) their value, for example in the client or in generated documents. Use non-localized attributes if you are not interested in the time component (e.g. birthdays) or if you want a date to look exactly the same all over the world. Otherwise, the date could shift because of time zone differences: a date and time early in the morning on April 2nd in Europe will be on April 1st in the USA.
DateTime field localization does not work the way you think it does (which I'd like to point out is not your fault).
See https://world.mendix.com/display/refguide4/DateTime+handling+FAQ .