hamster, they run a book and can do what they want that makes them the most money.Not sure about timescales but I would guess they have their own risk management systems.They also use sophisticated computer programs to help them.
I think we can agree that at some point a decision would be made to hedge or borrow or of course not.
Interestingly I traded a share through my cfd company(not direct) using a figure of 3978 long.I noticed the same trade went through as a sell via an 'o' trade.They were actually correct and the shareprice fell.I noticed that the same figure(trade at 3978) came through as a buy.More interestingly,This figure appeared no less than 4 further times whilst I kept open my long.When I finally closed the position the figure appeared a further time before never being seen again.
So not only are not all trades hedged but these companies actively trade your position until you close your trade!
30% of all trades on the stock market are via derivities(cfds being one of them)