Gonna echo the warning that fast activity like that isn't usually a sign that a culture is usable. Most of the time, you're gonna get a burst of activity, but it's going to be a random batch of bacteria fighting it out to see who comes out on top.

Eventually that's going to be yeast and lactobacillii. But it takes time for the culture to settle out into a well balanced and sustainable state.

What's likely is that in a day or two, you'll think it's dead. It won't be, it'll just be past that initial flurry as conditions smooth out and the desired microbes set up shop. It'll get slightly acidic and that's when the undesirable microbes get weeded out. Oh, you may run into some kahm yeast or whatever, but a stable culture prevents anything too bad from even trying to set up shop.

The general purpose expectation is that it'll take two weeks to go from initial mix to a usable starter, with a month or so being possible as the far end of that range. It's really unusual to have something that will be useful good baking before at least a week, unless you're starting with a donation from an established culture. Well, or you seed the initial mix with desired microbes. But that's essentially the same thing as being gifted a batch.

Anyway, as an aside, you have the right beginning. Unbleached flour is going to have friendly yeast in it. The stuff is everywhere to begin with, but whatever flour you have is going to be prone to having strains that are wheat ready. Otherwise it would be a different strain, you dig? Same with lactobacilli; they're everywhere, but the ones you find on any given food source is more likely to do well in it than something random, even if said random is from a different starter.

But hell, you can dump commercial yeast into an initial mix and get a sourdough starter that'll bake in roughly the same amount of time. It just won't have the depth of flavor since it'll be a predominantly mono culture. What makes sourdough is the eventual balance of microorganisms, not the yeast alone. So be patient. It's natural to want to get going and bake with your culture, but until at least a week has passed with reliable cycles of rising after a feed, you might as well just use commercial yeast. Let that sucker mature