Here's how to make a Roselle jam with freshly plucked Hibiscus flowers. It's very easy to make. It just requires a bit of time to wash, peel, boil and stir. Altogether it's right around 1 to 2 hours max, to completion.
Add a little bit of salt, and stir every so often for almost 1 hour
Wait until it condenses before adding in the sweetener
Stir over medium heat a bit longer if needed, until it's no longer liquid-y.
Video
Notes
This is the same process that makes Rosella tea from fresh flowers. After the first boil, remove the top half of water and that will be your Hibiscus tea. If you're making a tea at the same time, just add a couple more cups of water at the beginning. Then the remainder left in the pot gets boiled into the jam.