The Board has concluded that the date a commitment to extend credit becomes binding should be regarded as the date when the credit is extended, since:
    
    
        
        (a) 
         On that date the parties should be aware of law and facts surrounding the transaction; and
     
    
        
        (b) 
         Generally, the date of contract is controlling for purposes of margin regulations and Federal securities law, regardless of the delivery of cash or securities.