@OliI welcome to the KNIME forum. Date and Time variables are a standardized internal format that can be displayed in several ways but will internally remain the same:
You can extract the portions of a date and combine it back into a string in any way you like, but it will be a string. You will not be able to use date and time operations on that variable.
For presentations or charts it might make sense to convert a date/time variable. Or the report/graphic might be able to handle them in a native way and you specify a rendering in the process.