The problem isn't the Wait, but rather that your MBRM device is part of the If condition, and is also changed within your program.  When it is changed, the If becomes False, and the program immediately stops. 
  
To achieve your goal, you can use two programs, similar to: 
  
 
Program 'Part I'
If
       On Mon, Tue, Wed, Thu
       Time is 6:50:00AM
   And Status 'MBRM - 00.65.BE.1' is Off
Then
   Run program 'Part II'
Else
   - No Actions - (To add one, press 'Action')
Program 'Part II'
If
   - No Conditions - (To add one, press 'Schedule' or 'Condition')
Then
   Set 'MBRM - 00.65.BE.1' On
   Wait 5 minutes
   Set 'Fireplace - 00.47.B5.1' On
   Wait 5 minutes
   Set 'Stairs - 00.65.8F.1' On
Else
   - No Actions - (To add one, press 'Action')
 
  
Might another alternate be  
 
If
       On Mon, Tue, Wed, Thu
       Time is 6:50:00AM
   And Status 'MBRM - 00.65.BE.1' is Off
Then
   Set 'MBRM - 00.65.BE.1' On
Else
Wait 5 minutes
   Set 'Fireplace - 00.47.B5.1' On
   Wait 5 minutes
   Set 'Stairs - 00.65.8F.1' On
 
  
where the first condition is true and executes the 'then' which in turn effectively makes the first condition false and the program then reverts to the 'else'?