Stir all ingredients with a wooden spoon together in a large skillet until combined set over medium heat.
Stir occasionally. Cook for 15 minutes—during those last 5 minutes, stir constantly to monitor the setting of the jam. You should be able to swipe the spoon through the jam and leave a clear path for a few seconds (or dip the spoon in the jam and it should ever so slowly creep across the surface) as it thickens up.
Cool to room temperature before spooning into a jar, sealing and chilling it.
Look for culinary grade hibiscus in a Latin market or good spice shop like Oaktown Spice Shop. If using whole flowers, kitchen shears are the easiest way to snip them to smithereens.