I think typing all of that out.. made me say it 'out loud'..
I now have the solution

SELECT
 CASE
 WHEN [Open_Time] > AVG([Open_Time])...

Ok
So I have played with your solution and narrowed it down to this:
SELECT ID, [Open_Time],
 CASE
 WHEN [Open_Time] > AVG([Open_Time])
 OVER () * 1.5
 THEN 'Yes'
 ELSE 'No'
 END...

Firstly,, thank you for not flaming me.. and for the welcome 🙂

Secondly, thats for the solution.. 
I will work with what you sent me to better understand it...