Put the melon, sugar and pectin in a large non reactive pot. Squeeze the orange and lemon, add juice and rinds to the bowl. Mix and let sit (macerate) for 1/2 - 6 hours.
At least 10-15 minutes before cooking, place 2 metal teaspoons (tablespoons) in the freezer.
Place the pan over high heat and bring to a boil, reduce the heat to low and simmer for 5 minutes. Remove from heat.
With your stirring spoon place a small amount of jam onto one of the frozen spoons and let it cool for about 15 seconds. If the jam is still too liquid, cook for another few minutes and retest another spoon.
Remove the orange and lemon hulls and add the tarragon. Use an immersion blender briefly to blend in the herb.
Immediately ladle the hot jam into sterilized jars to the 1/4 inch line. Process for 15 minutes in a boiling-water canner.