Hi,
Benefit of creating the filter at universe level is reuse the filter in multiple webi reports without create prompts at webi query level.Other benefit is when requirement to filter the data in webi reports based on the single date/month year (without entering the range) and pull like last month data,year,week data.In this case user will enter only one date then webi report will pull the data based on the date upto 30 days/year data.
But in your case where you are defining date range then you can create universe filter or webi level prompt.both are same.it's upto you where you are more comfortable.
Universe filter:Right click on the universe class->new filter->select the filter type "Business"
Webi query prompt:Drag the object in the webi query filters panel and select the operator and select as prompt.
Amit