set_input_delay constraint

I don't know how it's failing and what you have now(I assume the outputs are registers, they just have combinatorial logic before they go to the pin). If so, registering them would make them have a faster output time. Of course, the fitter can use IO delay chains to slow down the output time too, if it deems it necessary for hold. It is standard practice to register your data outputs, but I don't know the specifics of your situation well enough to say if it will help. It will probably help, and should not hurt.