I’m not sure if there was a question there? If I follow correctly I think you are saying you do not want to display date fields on the report, but you want to group and/or sort based on the date fields? If that is correct, then there are no requirements stating that you have to have the field present on the report to use it in grouping or sorting.
If I am incorrect could you also explain what you mean by “as per”. As per is considered jargon, or old english used for legal documents. I just want to make sure that I follow your meaning, and therefore can try and provide a helpful answer.