The ships never got within gun range.
And it would not make a difference, if not a single warship showed up. Davis was not going to allow Sumter to be provisioned by any means by anyone. Any attempt to bring provisions to Sumter would have met exactly the same result.
He would reduce the fort by force, before he would let it be provisioned.
If you would honestly read the message traffic for both sides, you would realize that yes, it would have made a very big difference. There would have been no attack on Sumter at all but for the arrival of those ships.
See Beauregard's message to Anderson asking him to refrain from firing upon them if they got into an engagement with the ships.