For all of the 'finding Gallifrey is the Doctor's reason to travel', he didn't actually get around to doing a great deal of it last year now, did he? Unless he had a quick nose around for it during those two weeks when he was getting coffee, he apparently never gave the matter a thought until Missy volunteered the information that she knew where it was. Admittedly, having just spent a thousand plus years having to listen to them bitch at him through a crack in the wall might have put him off the task ever so slightly, but if you go to all the trouble of setting up an ultimate goal in your travel/quest format, you probably need to at least tip your hat to it once in a while. If nothing else, it would have made Missy's revelation about knowing Gallifrey's location a bit less jarring if fans had been reminded once or twice over the series that they actually cared where Gallifrey is. That would certainly have given a greater edge to the Doctor's frustrated smashing of the console when it turned out that Missy had lied.