I use 3470 regularly and I find that I typically see signs of fermentation in less than 24 hours and often within 18 hours (typically I pitch around 48F and set my fermentation temp to 48F). Here are some thoughts (I’m sure someone else has already posted these, but here it goes anyway)...
Inevitably store bought yeast is going to be a little bit old: there’s a decent lag between when the yeast gets packaged, when it gets delivered to a store, when it gets purchased, and when it finally gets pitched. Because of this, it can take some time for the yeast to “wake up” and the start of fermentation can be sluggish. If you aren’t already making a starter, I highly recommend it. Not only will it wake up your yeast it will also help insure your have enough cells (more on that below). Chris White’s yeast book has wonderful and easy to follow info on making starters. On a related note, if the yeast is being pitched out of a packet that was taken straight from the fridge the yeast will be much colder than your wort and so it will take even longer for it to adjust and with that more of a lag.
Second, I know others have commented on whether or not you need to aerate, but I would highly, highly recommend aerating or, if you can, oxygenating. Once again I will point you in the direction of Chris White’s book in that it highlights the importance to having enough oxygen early in fermentation. Of the handful of times I have had slow starts with 3470, a few of them were due to not enough oxygen.
Finally, double check that you have enough cells. The few times I have had lags with 3470 most of the time it was because I didn’t have enough yeast cells. Mr Malty has a great pitching calculator and Chris White’s book has an easy to follow formula. Insuring you have enough cells will help you start fermentation better. It will also help insure you make excellent lagers.