Creating a table contains Avg Days prior Closing per BU

Hello, 

I have a data model below where I have the fact tables that links to two dimensional table both have many to one relationship.

DIM_COST_CENTER does not have a relationship to DIM_OPPORTUNITY.

My goal is to have a table like below: 

Business Unit is from the table 'DIM_COST_CENTER'

Avg Days Close should be the difference between Closed Date and Created Date from table 'DIM_OPPORTUNITY'

I wanted to create the Avg Days Close within my fact table but I could not able to call the date fields from 'DIM OPPORTUNITY'

And create a table for Avg Days Close per Business Unit.

Please help how do I do it.