srnity: Hi, you are very kind to look after your friends dog for them.
12 hours does sound like a long time for the dog to be left in the crate though.
My advise would be to leave a bowl of water & a couple of toys in there for him to play with. Preferably a toy to chew to keep him busy & stop him getting bored?
Do they usually leave him in there over night? If so atleast he is used to the crate for longer periods.
Hope thats a little bit of help.