“I believe MM's are forced to close out their short or long positions before the close on Fridays, by rule.”
No, not sure where you got that.
Even if the shorts are partially hedged with options that is really more of a doomsday prophylactic, not part of their basic strategy. If tutes accumulate they will want to get out of the way. Or if they sense news coming.
News 
Market Data 
Discover 
AI
