How long are the classes?

[erinellii]

No: HPFGUIDX 79647

anna wrote:
  I think that a 'single period' refers to just Gryffindors (or 
Ravenclaws/Slytherins/Hufflepuffs..  one house) while a 'double 
period' refers to having a class with two houses such as Gryffindors 
and Slytherin together (potions, for example).
 

  
  I think that too, but it raises some questions.... Why do they 
never call the Care of Magical Creatures class "double" - it includes 
Slytherins and Gryffindors, right?  In fact, the only class I 
remember them ever calling double is Potions.  And that would make 
sense if double referred to the length of class, because there are 
probably some potions that it takes an extra long time to make.  Wait-
 maybe they did have double Herbology one year...

does anyone else have any insight on this?

Erin