In our state (MT) a contract has to be placed on MLS within 24 hours.

In my board we must place it in the MLS, but it's listed as pending with the number of hours for the kickout clause--ie 24, 48, etc. so I don't hesitate to show houses pending contingent upon the sale of another house. My clients know we might be waiting on pins and needles for a couple of days while the original buyers are making a decision to remove the contingency. About 75% of the time my clients get the house.

In my state it is required that contracts be immediately entered on the MLS - otherwise we would not have disclosed it! On the agents' more complete version of the MLS it's shown as contingent on sale of another house with a kickout, but I don't know if it says how long the kickout period is. On the consumer version of the MLS it just says "contingency" but doesn't specify what kind.

Our contingent offer went kaput (long story) which was fine with us because there was no sign that his property was going to move anytime soon (there's a lot of inventory in his town and his house is OK but nothing really special and did not seem aggressively priced) and that was just making things difficult for us. The week after that contingency tag went up we had two showings - one generated the offer from the bargain-hunting nutjob - the two weeks after that we had had one showing per week, and then last week we had NONE. Nada zip zero. The calls had dropped to nearly nothing too. I was beginning to get very frustrated and it really was impetus to tell the guy to take a long walk off a short dock when he began to get difficult. I think he thought he had us over a barrel and he didn't. We signed the offer release Friday morning, dropped it off at the realtor's office at noon and asked his assistant to put it right into the system so we knew it would get done! Within hours of the contingency tag being removed, there were multiple calls, and we had two showings within 24 hours . More showings today and I'll bet there will be more calls on Monday. We're hoping for a busy week and plenty of warm bodies through the place at the open house scheduled for next Saturday since we'll be at 60 days on the 23rd. :-p

We've decided we're not accepting any more sales-contingency offers. Maybe if they have a binding contract on their property, passed inspections, the whole works - and even then it had better be a very good offer. We learned our lesson, lost weeks of prime selling season!

Oh, and when we looked at a couple more houses in the last few days I asked the selling agents if they showed houses with contracts with kickouts to their clients. One said only if the client found it him/herself and asked to, the other said no, especially in this market where there are plenty of other houses to look at.

It is required in my area to report it to MLS within 24 hours. Our MLS contract states the sellers must follow the rules of the MLS. For this reason, depending on the market, I will recommend my sellers not accept a contingency offer to keep the house fully active. I don't think it benefits a seller at all to accept a contingency offer in a buyers market. It holds your house up, stops others from wanting to look at it and there is no guarantee that the buyers house will sell or even if they will get to the contract stage on your house. They could simply change their minds. Its a win win for the buyer and a big chance for the seller.

Now since so many will take this literally, of course there are exceptions, ie: the house has been on the market forever with no offers, it has a horrible location and any offer is a good offer, etc.

Most MLS require disclosure within a certain timeframe.
However, a seller can insist on not disclosing the contingency in the MLS, after all, the agent is working for the seller in the sellers best interests, right?
If the seller or agent is willing to pay any penalties levied by the MLS board ($100 here), that is a chance one can take.

In my MLS there is no Contingent status. Only Pending. MLS require to update status in 24h. I usually do not and pay $100 penalty

I don't know if it's the law in my state (Iowa), but I did notice that when we made the offer on our current home with a 72-hour kickout clause that it was added to the listing. It simply said "72-hour clause" at the beginning of the house description. I do not know if the previous owners' showings dropped off, but I do know there were at least two open houses held between the time our offer was accepted and we closed on the house.