Overheating a pizza stone?
As always, it comes to the meaning of "OK". The most likely scenario here is that the stone's life is shortened and it cracks. It's impossible to say when this will happen, it could be soon or it could stand up to hundreds of pizzas. 

So if for you it is worth it risking the stone, you can do it. If you want to avoid with certainty the stone breaking after 4-5 uses, don't use it outside of the parameters determined by the manufacturer.