Actually, given the amount of dialog and compressed nature of the Moffat's stories (lots of story in an episode) for both Sherlock and Who, I wouldn't be surprised if his scripts are longer than the typical script for similar length episodes. Plus, the thought and editting that goes into making a full script as compact as possible must take considerable extra time.
Thing is even with the extra time he still doesn't get them done on time. They're literally only making one episode in nine months and the production departments were still waiting on the Anniversary script four weeks before shooting was due to start.