yeah, second that...it's pricey, especially for what it is (essentially a lunch counter) and its location (though easy to get to on the A to Nostrand Ave. and a block and a half walk from the train), but the pastrami is damned good, among the best you'll find in NYC these days.
As far as hours, I think they are pretty much daytime only, probably close around 5 or 6, but I'm not exactly sure other than that they are closed in the evenings.
I love the place. That's the only place I order my corned beef lean because of the fat content. It still comes out very moist, but not greasy when lean. And the taste is great too. They also make a great season brisket which I have ordered for take out and thirty minutes later the meat was still moist. David's seems to be a combo Kosher style deli and Halal soul food place. I like it a lot. I'll go there for deli before Katz's.