Why do you think that my cooking time is so much shorter than yours? All of the
jams I have tried have taken usually less than half the cooking time - and I
really thought I was cooking them at a "mild boil". I'm wondering if I'm
stopping before you would, which makes me also want to ask how "set" is a
jam supposed to be? I tend to like mine a little softer than commercially
Timing is so personal, there is actually no wrong amount of time as long as it reaches a boil. There can be a hundred reasons your time is shorter and it's all fine. Yes, your stove could be hotter maybe gas as opposed to my lame electric. The fact that you like it softer is a huge reason - in Afghanistan I had to drop my cooking time by a lot because they like it more like a spread than a jam. They don't spread the jam with a knife or spoon but rather pour it on a plate and then scoop it up so it has to be plenty soft.
It also has a lot to do with the fruit. The riper the fruit, the less pectin and the longer cooking time if you're not using pectin in the recipe like me. Your fruit could be less ripe which is great, you generally want a mix of about a quarter not so ripe to add that pectin. I make so much jam and I'm a natural cheapskate so a lot of my jam is made with the fruit that they're going to pitch from the farmers market. I don't really have to cut the stuff sometimes, just sort of smoosh it into the pot :) Not really, but I have a hard time resisting that closeout bruised fruit at the end of the morning and end up coming home with lots of cheap really ripe sweet fruit. The jam is to die for, but needs a long time to pull itself together.