Many developers are very active and start the process within seconds (as you have discovered). So within a short time you will have gotten the highlight areas underway but you need much longer times to get density in the shadow areas.

So now you have an insight into the problem some people have with highly active developers and some film combinations giving them blown (hot) highlights when they develop to get the right shadow density.

If you had realized your mistake you could have washed the film to remove all traces of stop and then started the process over.

Thanks for an interesting post