Prepare a water bath canner or fill a large pot with water and add six half-pint jars. Bring to a boil and set a timer for 10 minutes. After 10 minutes, turn off the stove and keep the jars in the hot water until needed. Once you remove the jars, you can add the bands and lids for a few minutes until needed.
Using kitchen scissors, snip off the stem and green petals of the blossoms at the base. You only want to use the yellow petals. Give the petals a quick rinse, you don't want to wash away the flavor, or their beautiful color.
Pour cold water into a large pot and add petals, orange slice, and lemon zest. Simmer over low heat for 5 minutes; remove from heat. Once the tea is room temperature, pour it into a 1-quart mason jar or another container. Screw the lid on and steep the tea for a few hours or preferably overnight. It does not need to be kept in the refrigerator.
Strain the steeped tea using a fine-mesh sieve, coffee filter, or my personal favorite, a soup bag. Squeeze all the liquid and flavor out of the petals and citrus, and get every last drop! Discard the flower petals and citrus peels.
Measure the liquid and make sure you have 3½ cups of liquid. If not, add some water to bring it up to 3½. Pour the tea back into a large saucepan and add lemon juice, pectin, and sugar, as you whisk. Once the mixture comes to a rolling boil, set a timer for 2 minutes. After 2 minutes, remove from heat.
Skim foam, if necessary, then ladle the dandelion jelly into sterilized jars, leaving ¼" headspace. Run a small knife along the edges of the jars to release any trapped air bubbles. Wipe the rims of the jars with a damp cloth or a wet paper towel and hand-tighten the lids. Avoid over-tightening.