Gizmo's ears popped up around twelve weeks also. I don't even remember when exactly. It's almost as if it just happened overnight. I have seen some corgis though where one ear pops up while the other remains down for a little longer.
Moose's didn't stand up until this past december/january when he was 5 or 6 months old, I can't remember exactly, but it took awhile. he still has semi floppy ears now. His one ear popped up and the other was down for about 3-4 weeks.
If he gets to be 12 weeks and they're still not up, tape 'em.
My boy puppy who went overseas, Kipling, had the largest ears I have EVER seen on a puppy and I had to tape him for over a month! A typical Pembroke ear can often be taped overnight or for two days max and they'll be up. Cardigans often require a couple of three-day sessions. Kip was definitely an exception, but we DID get those ears up!