I wouldn't delay changing the oil, but it shouldn't hurt the engine. The ATF has lots of detergents and will break up any sludge or build up in your engine. That could cause oil leaks and will make your engine much cleaner inside. Sometimes, a quart of ATF is purposely dumped in the crank case to solve a ticking lifter (it cleans out the dirt that may have clogged the lifter). But of course it is not recommended. Change the oil soon as you can, but there should be no permanent damage.