How to retrieve a MAPI property value from an exchange mailbox

I'm new to using Power BI, using the free desktop product, but have experience using VBA with Excel and Access. I'm working on generating reports from an Exchange Online shared mailbox where I need to get the minutes between the date received and when the message is completed. The message is considered completed when it's placed in certain folders. We were using the LastModifiedTime value for the calculation since once the message is filed, nothing else should change it. Unfortunately there must be some backend process that ran the other day at 4am and changed all of the values for the LastModifiedTime. 

So now we're looking at marking the messages complete when they're moved to the folders. If we take this approach, we can get the TaskDateCompleted from the ExtendedProperties but it doesn't include the time.

By using MFCMAPI I can see the PR_FLAG_COMPLETE_TIME (PidTagFlagCompleteTime, ptagFlatCompleteTime) tag is 0x10910040 and gives us the time we need. However, all the examples I've found for getting this value are using VBA code in Excel and I can't figure out how to get it using Power BI/Power Query. 

Appreciate any help anyone can give me. Thanks.