That is interesting, my memory had me convinced it was hours until they were even touch dry.
There may be some variation between brands and formulations. In fact, I think I recall such. I mostly used Floquil, which painted on very thin and dried fairly quickly straight out of the jar, but most people I knew used Testors, which was much thicker stuff and took longer to dry. Not sure where Humbrol fell on the spectrum. Additionally, I wasn't necessarily waiting until a coat was completely dry, as I did blend shades on the model to a certain extent, even then. I'd make sure the base coat was good and dry, but for anything else, touch dry was plenty good enough, since I was either blocking in adjacent areas or blending related shades. I think I probably also waited longer before painting fine details over the primary colors.
When I was attempting to recreate the same workflow to batch paint imperial guard and eldar a few years ago with acrylics I found I could do it, but I had to paint very, very quickly indeed so that the first miniature wasn't completely dry before I started blending in the middle shade. (I would typically use a three tone process for shadows, midtones, and highlights of a given color. Sometimes I do it a little differently now, since I started using inks sometime in the 2000s. After I made the acrylic switch.)
All of it has changed in recent years anyway, thanks to health discoveries and new regulations and so forth. (Testors acquired Floquil's parent company Pactra-Polly S some years ago and completely discontinued the brand, allegedly amid health concerns.) I couldn't find the same stuff anymore if I tried, and whatever is left probably paints differently. There's some new brands now, and I think there's wider availability of UK enamels in the US now than there was in the 80s, so maybe I could try some of that Humbrol goodness.