Note: answering my own problem to help others in future.
I\'m reading a CSV file with OleDB:
DataTable csvTableSchema = new DataTable();
Turns out OleDB uses nn instead of mm for minutes in DateTimes.
So the correct syntax is:
DateTimeFormat=dd MM yyyy hh:nn:ss
Ref stashed in the internet: http://forums.codeguru.com/showthread.php?333106-schema-ini-DateTimeFormat-legal-values
I couldn't see this in the official documentation: https://docs.microsoft.com/en-us/sql/odbc/microsoft/schema-ini-file-text-file-driver