An 'Aggregate Query' in query design view is the big E symbol (Sigma) - - but if long date has minutes I think, though can't remember off hand, it would be too fine to be the grouping field - - but let's say you have a simple date field - and then it will group by date, and you can change the default 'group' parameter to count (or sum or avg or etc) - - so that is an Aggregate Query that you want to research. The term 'grouping' is more often used in Reports where that is a specific feature.

It is sometimes easier to first make a simple Select Query that establishes the date range - and returns let's say: >= 1/1/15 AND <=1/7/15 for one week - - save that as 'DateRangeQuery'. Then when you make your Aggregate Query use this as the starting point record set, rather than the table itself, so you are working with just the range that you want.

Hope this helps.