No bubbles!

Started my second batch of beer on Saturday, an IPA. Rigged up a blowoff tube after my last experience (see lid blew off of bucket and covered the basement with krausen)... Fermenting a lot cooler than last time now that I know what can happen to your flavors if its too hot. In 2 days I have yet to see a bubble come out of my blow off tube ( I know that means nothing), even though I have noticable krausen forming. Is there still a chance this will take off and I will need the blow off tube? Or would I be safe to switch back to a 3 piece airlock at this point?

If you have krausen it's fermenting. If it's not near the top, you may not need the blow off tube. I never use a blow-off tube, since I have plenty of headspace. If you have enough headspace, you won't need a blow-off tube either. If you don't, well, then you need the blow off tube!

My question wasn't so much is it fermenting, as I know that it is.... I've read on here that having pressure inside the fermenter can stress the yeast? Therefore its my thinking that if the blow off isn't needed, it would be beneficial to move back to the 3 piece (less resistance for CO2 to leave the bucket means less pressure). However, I don't want to end up with another mess.

With a bigger (OG 1.062) beer fermenting at ~65-66 degrees (ambient 60), will it take off like the last one did and end up needing the tube?

There's no reason to switch it at this point. The reason for a blow off tube or airlock is to let the co2 escape and keep o2 out. It's a vent basically. The benefit of a blow off is it lets larger volume of gas out and allows for krausen to leave if ferment is aggressive enough. I don't see any benefit to switching to an airlock. I ferment all my beers w a blow off.

As long as your are within the yeast's optimum range, you likely have fermentation. The thing about cooler fermentations is that they are not only less active and slower, but they are also much cleaner as a result. You would expect the cooler fermentation to be less active than the warmer fermentation you previously experienced, and that's a good thing, because less fusels and esters are being produced. This cool fermentation should take longer and be less active, but you'll also have a cleaner, better beer as a result.

Patience and gravity readings are the key here Give it 2-3 weeks, then check gravity when you are ready to bottle/keg.

Many people use a blowoff tube and will wait 2-4 days before deciding to remove it and replace it with an airlock.

You can do either. It's simply a matter of preference.

A blow off tube is just an airlock.

I often don't even bother replacing it with an airlock and just it on for the whole time.

I swapped it back to the 3 piece this morning, it is bubbling madly... still not sure why the blow off tube never bubbled, not even once. This fermentation is much more under control, and will hopefully create much better beer than the first one did.