How Long Does Oven Spring Last?

I've heard two common explanations of oven spring – pop a well-proofed and shaped dough into the oven and:

1) The existing gas pockets in the dough expand thermally (or alternatively that liquid water vaporizes and expands).

2) The yeast increase activity due to increased temperature.

Regardless of what's going on, my question is how long should it take and to what extent fast delivery of heat helps. In both cases, the rate at which heat is delivered doesn't seem to matter. The yeast will get hot, the gas will get hot, the whole thing gets hot in time. In fact, for process (2) the longer you were to hold the loaf's internal temperature in the low 100s F, the more gas the yeast would produce. The only reason I can see for fast delivery of heat is to achieve oven spring and start setting the bread before it spreads too much.

What brings this thinking on is that I usually bake my bread on a preheated cast iron pan, but it was recently occupied so I just put the bread on a baking sheet covered with parchment. It took 30 minutes for the bread to complete its rise in the oven. When I put it in the hot pan, it usually takes about 15 to 20 minutes. Either way, neither of these are very fast processes, certainly not the speed at which I could watch the loaf grow dramatically before my eyes (unless I was very patient) as I've heard some people say about their oven spring.

Am I not getting oven spring? Does this term refer to a much faster rising? Or is the rising taking place over 10s of minutes and maybe fast delivery of heat doesn't make such a difference?

The only significant difference I could observe between my loaves baked in the preheated pan and my loaves baked on the baking sheet was that the bottom of the loaf on the baking sheet was a bit underdone compared to the top of the loaf.