Normally around 8am. The trick is choose something dealers aren't interested in. Most are after gold, military, or Art Deco porcelain/china. Very few bother with Art. The secret is only buy original Art, and look at the back of the painting, if it's been framed by a gallery, chances are it's worth something.
My rules are, if no gallery, always pay less than £5. If there is a gallery sticker, pay as much as £5, or, in extremely exceptional circumstances, £10, never any more than that.
I have a beautiful painting in my lounge that cost £1.50.
Go for the house clearance guys, they normally have a lorry/van and all manner of stuff.