They took three months to grow, which is, as Dr Post points out, "faster than a cow".
Lost a lot of respect for the man here. If it took him 3 months to grow a quarterpounder he is not even in the ballpark, hell it isn't even gameday. A bovine will grow more than that in a day during development. If a cow only produced a single quarter pounder this would be true, but sadly this is just dishonest on every single level.
Does he have a plan to grow fatty tissue as well or will his burgers be doomed to taste like **** and have limited nutritional value forever?