After a month it will be possible to place orders, but it will not be possible to see the orderbook or the price history so you will have to look that up on bitsharesblocks.
After 2 months or so there will be full trading. This was according to BM in the dev hangout. We can probably assume that these are estimates that only apply if no issues whatsoever come up during that time. There'll likely be plenty of unforeseen stuff so we end up with doubling the estimated times.
Another interesting thing is that the web wallet might have trading out of the box. The yunbi web wallet is coming very soon and it might have trading right away. That would be completely amazing.