Getting concerned

OK I brewed a Midwest kit -Excelsior Altbier.
I used a Wyeast 1007 German Ale smack pack. I did a starter, pitched at 60 degrees, held that for 12 hours then moved it to 52 degrees for 36hours. Swirled it everytime I walked by. It looked and smelled great.
I cooled my brew to 60 degrees, aerated well, and pitched the starter and moved to the 52 degree basement. It took 24 hours to drop to 52 degrees. The temp range on the yeast was 55 to 66F.
I guess you can see where this is going. It's been 72hours and no activity thru the air lock. I know the cooler the fermenting temps the slower the rate of fermentation. I am sure the bucket lid is tight.
Do I have a problem?
SG when starting was 1.042
How long should I wait to do another hydometer reading or should I just forget it for a couple of weeks?

Your beer is fermenting. It just takes time and the airlock tells you nothing.

It's easy to get excited if you haven't done this much before. All will be well.

I would walk away from it for a week or so. Just because your airlock isn't bubbling away doesn't mean diddly. I've had plenty of batches that the airlock didn't bubble once and yet it was fermenting away.

Wait a week and take a gravity reading.

I wouldn't even touch the beer for a good two weeks in the primary. Lower fermentation temps will obviously slow the rate of fermentation for you. Just let it sit for a while and after two weeks, take a hydro reading. You should see movement downwards on the SG, but may not actually hit your target FG for a few more weeks. That's a somewhat slow moving yeast at those temps, but will be very tasty and clean when finished.