how long to wait for buyer's attorney?

The apartment is not yet "in contract". Therefore, it's still on the market, and you are free to continue to show it.

After two full weeks, contact the prospective buyer and ask what's up.

Have your attorney call the buyers attorney and get a schedule. Coops take longer since there is more for the attorneys to see. Also if the coop is dragging their feet and not sending the buyers attorney the information that is requested, that will positively slow things up. Your attorney should already have all the documents that are needed. NYCMatt is correct in that the coop is not in contract and therefore you can still have it on the market.

After two weeks, you should absolutely schedule an open house. No question. Don't put all your eggs in one basket.

The attorneys ought to be talking and the status not be a secret. If there is a hold up, there's a chance you could help by, for instance, nudging the management company if they are dicking around and not providing what is needed. Word should get back to you rather quickly though as to what the status of the deal is from the buyer's perspective. When I was buying a year or so ago, once my offer was accepted, my attorney needed to iron out some glitches with the managing co. to arrange seeing the minutes, financials had to be obtained and reviewed, and the contract terms had to be negotiated back and forth a bit. I'd say this all took about 7-10 business days. The buyer's attorney may have had some other unmovable commitments, too, that gobbled up a couple days.

As a seller, you should absolutely be scheduling open houses and showing the place and not keeping that a secret. Until you have a contract in hand, you don't want to be wasting time not marketing your place. It also keeps some heat on the prospective buyers. Nothing rude or wrong about continuing to show the place. The buyer's agent and attorney should know this is pretty standard fare.

Schedule an open house. Old rules were that attorneys wouldn't send out more than one contract on a home, but in this market, I see no problem with that.

I'm a buying and I get the same heat from the seller's broker. They annoy...err..call every day to check whats up.

I'm like, chill man, unless theres a contract, the apartment is up for grabs.