I don't think the 50th thing will link back to Clara much, if at all, purely becuase I'm sure he'll want to make the episode more firmly about the Doctor himself.
As a side note - the fact Matt's chopped his hair must mean he's done it for his new movie role, as his hair is an iconic part of him in the role of the Doctor, and part of the reason he was hired. That means, presumably, they've either wrapped or are wrapping soon. Considering they've wrapped after a month, I again doubt this'll be more than an hour. The End of Time was filming for ten to twelve weeks, for instance - that was for a two parter, 60 and 70. Your average two-parter in the series (90 minutes, 2x 45m) films for 6-7 weeks.