This way you can make multiple offers within a relatively short period of time, and not worry about having too many pending offers on the table. Plus, you'll be able to leverage the odds in your favor, and you can go with the best accepted offer.
Because nothing is sealed contractually until the addendum from the bank is signed by the buyer, I'm seeing the additional case of buyers walking away (perhaps a change of heart or inspections that revealed higher costs than they were prepared to put out). All that said, there is no set standard in the time-factor for REO properties being exposed, available or accepted.
Hope that helps!
The scenario you described is common but not ubiquitous.