Ok, now that I've discredited the value of anything here forward... I believe that there might be something in contract law that requires that an offer be made in good faith, as in the buyer is going into the contract with full intent and is wanting to buy THAT place.
Yes you might be able to use an "out" like HOA docs, but I believe you might have nullified the contract before that right begins if you have 2 places under contract with no intent to perform on BOTH.
As for ethical, I also believe the the Realtor's code of ethics precludes agents from doing that.
Anyhow, why not just put a 5pm deadline and make the 2nd other offer at 5:01pm? There is nothing wrong with that, and I do that all the time. Or you can make it nullify in an hour and tell them "technically the offer is no longer good, but you can still 'counter' by crossing off the deadline and sending it over." At that point it is a counter (even if the price is agreed to)
1) Buyers offer $500k for property 1 , deadline in 1 hour
Now the quesiton should be "ok, give me HOW you CAN do it" (I hate "no" answers, I like "ok, tell me how I can effectively do what I want to do")
If you are an investor and disclose your intent to use multiple offers, you might be able to put "Purchase is placing offers on multiple properties. This offer is nullified upon acceptance of another offer" that MIGHT fly, but you would have to ask an attorney.
Frank Borges LL0SA- Realtor/Broker FranklyRealty.com