There are a couple of discussions on a similar topic in the eazyBI community:
Janis, eazyBI support
The best way is using Time month selection on Pages. However, if you do not want to use Pages selection and would like to address a particular Time member in a calculation, you can use tuples.
Here is an example, how to address August'2018 in a tuple:
[Time].[Month].DateMember('01 AUG 2018'))
The tuple above will retrieve you hours spent for August (Aug 01 2018 to Aug 30 2018)
You can address periods more dynamically as well. Here is an example of how to retrieve hours spent of previous month:
Daina / email@example.com