How to Map the "Expires" date column in the Search Schema for SharePoint Online (Office 365)

With SharePoint Online you can’t create a New mapped search column as simply as SharePoint On-Prem. With SharePoint Online it is best to use one of the pre-created mapped search columns, created for you, by SharePoint to use. I.e. RefinableString, RefinableDate, RefinableInt and RefinableDecimal.

For this example I will be Mapping this column, for my whole SharePoint Online environment, so all my Site Collection can access this Search Mapped Column.

1. Goto your SharePoint Online Admin Center
2. Click "search" on the quick links menu (on the left)
   
3. Filter by "refinabledate"
   
4. Click "RefinableDate00"
   
5. You can see that this column is already for searching, and has been configured to be a "Date and Time" column type
   
6. Add an Alias to this column. This will inform other and "future you", what this column is for. 
   Alias: AnnouncementExpiryDate
   
7. Scroll down to "Mapping to crawl properties", and click "Add a Mapping"
   
8. Find "Search for crawled property name": Expires
   
9. Select "ows_Expires"
   
10. Click "OK"
    
11. Click "OK"
12. To see the column mapped, filter again by "refinabledate"
    

Now you just have to wait for the SharePoint Online Crawl to run :)