You can set the default display format in the column properties (when you are creating an analysis with that column in it).
It can be set for the column itself or for all columns with the same datatype.
I think your prompt values will be show in the correct format, but I didn't test it myself so not sure.
As an alternative have a look at: https://support.oracle.com/epmos/faces/DocumentDisplay?_afrLoop=343936076961993
I was able to identify the issue. I had to change the localedefinitions,xml config file and change the date format there.