Cool! I just brewed my 2nd ever batch this past Sunday and have this same situation. My first batch began bubbling about 48 hours later, but here I am at 72 and there's no sign of it.
So since I'm on the topic of my 2nd batch, I'll just share my experience with it here.
I'm using "Brewer's Best" recipe kits. First one was a German Oktoberfest. I followed the directions straight through and added the yeast directly from the packet to the wort after it had cooled and I had added the extra water to bring it up to 5 gallons. I saw bubbling after 2 days and it kept bubbling for a couple days after that. All was well. The beer turned out great.
Then I read through this website:
...and learned about rehydrating the dried yeast. The Brewer's Best directions just say to add the yeast. I looked at the yeast packet of this 2nd batch, their Scottish Ale, and saw that sure enough, it did have instructions on the packet for rehydrating before adding it to the wort. The first packet wrapper is long gone and was a different brand/labeling of yeast, so I have no idea what that packet said, if anything. I followed the directions on the packet.
I also upgraded this 2nd batch to using a much larger brew pot. The first batch was close to overflowing in the smaller pot, so I was a it stingy on the heat that time. After adding the LME and the DME, I boiled it for a very long time just trying to get a nice, big rolling boil, but I got only a bit of churning at the surface. Maybe our gas stove just doesn't have the thrust. Anyway, so I added the hops, followed the timings, turned off the boil and let it cool. When it was close to temp, I rehydrated the yeast. It said to do it for 15 minutes and don't stir until afterwards.
Last time, I added straight tap water to the wort. This time I tried first boiling 2.5 gallons ahead of time and set it aside, then 2.5 gallons for making the wort. When I put the two together, I had ...only 4 gallons? I had lost a whole gallon of water into steam during the prolonged LME/DME boil! So I just went ahead and added an extra gallon of tap water (we are on a well, no city water chemicals) to the wort.
After 15 minutes, it did have some bubbling in the yeast, but the glob of yeast was mostly dry in the center. The water hadn't soaked through. So I mixed it just a touch to get all of the yeast wet and let it sit for another 15min. Then I stirred and added it to the wort. This time I stirred the wort quite a bit to get the yeast nice and mixed in. Last time I just swished the spoon around a couple times, thinking that it had a few weeks to mix itself.
So I didn't bother going into the basement for two days, this time. Here it is going over 72 hours and no sign of bubbling in the trap. I peeled off the bucket top to have a nosy. It smells like it's fermenting, so I think it will be alright, though I do like seeing that trapped getting a good workout. Maybe I somehow missed that part during those first two days???
If I did anything stupid, please point it out. I know I'm making too many changes in my process from one recipe to the next, but I'll get that hammered out in due time.