It depends heavily on the sort of date time objects. As a rule of thumb we always use non localize date time objects on things like birthday where time is not an issue. The only why to get this right is to make the attribute non localize and use a microflow to adjust all the dates . It is wise to first download your database and check with pgadmin your data. It gives you a good feel on how the hotfix microflow should look like.
The result should be that all the non-localized dates in the database should have an UTC time of 00:00.