Quick fermentation, then almost stopped.

I have a copper ale (starting gravity: 1.058) that took off like a rocket within 12 hours of pitching Safbrew S-33. It's my first all grain brew, and also the first time I've rehydrated before pitching. It got going quickly, so much so that it bubbled almost half a gallon out of my carboy through the blow off tube (that's never happened before). It was still bubbling and churning like crazy when I checked on it last night.

Now, this morning I checked on it and it's slowed significantly. There are still bubbles coming out, but it is nothing like it was last night. Is 48 hours (maybe a little more) long enough for a 1.058 OG beer to be nearly finished? If so, that S-33 must be some killer yeast.

So, should I be worried? I'm hesitant to take a hydrometer reading b/c I want to long primary this batch and not risk infection. Thoughts?

It's possible that you pitched while the beer was a little warm. This caused the yeast to take off like crazy and do the bulk of the fermentation right away. Let it sit for a few weeks and take a hydrometer reading. It sounds like all is fine.

The wort was just below 70* when I pitched, with the rehydrated slurry at around 85*. Ferm temp has been a stable 60*, which is actually toward the low end of the recommended range for this strain. I have a sticker thermometer on the side of the fermenter so I know I've been right in line with the temp guidelines, and nothing has changed since it started. ???

There's absolutely nothing wrong with your beer, only your perception of what your beer is and or should be doing...the answer is right here;

https://www.homebrewtalk.com/f39/airlock-activity-gone-before-5-days-210459/#post2460863

Yeah, this is not unheard of. I just had a stout that started at 1.100 get down to 1.030 in 48 hours.