I must admit that I am new to the OBIEE world and I really wish I can help people that are starting with this Oracle product to save some precious time when dealing with Calendar dimensions.
I have created a Calendar dimension in my database with a field "DIA" to be DATE. This dimension is meant to replace one that was already in place, same content, but more fields. I have imported the table in the physical layer, mapped it to the logical layer, but when I run the dashboard I kept on seeing date fields with DD/MM/YYYY hh:mm in the calendar prompts.
I spent quite a lot of time (call me dumb!) to find out that the answer was as simple as replacing the DATETIME field with DATE.