About the sitting overnight: Edna Lewis and Scott Peacock’s recipe called for that step, and I’d guess you could skip it if you wanted. Although I don’t know the scientific reason why, here’s what I noticed: as you let the berries macerate in the sugar, they release lots of juice. Cooking it the first time draws out more juice from the berries and causes the mixture to thicken. As it sat overnight, it thickened even more. My best guess is that since you don’t use pectin, the sitting helps the mixture to jell properly without having to cook it for hours and hours (which can interfere with the strong taste of the berries).

Don’t wait too long to start jam-making; I wish now I’d started years ago!