Well its not like he was able to have access to a terminal anytime he wanted. Only that roon had one that yui had opened. And he only had a few mins to do anytin with it. He got lucky he was able to retreive her origianl data and made an item out of it. Besides I have a feeling hacking the network of SAO would take him a while. I suspect he's really good with computer stuff but knowing how they set diffrent things up, he wouldn't just be able to walts right into the network without any problems.