Prepare canner, jars, and lids. Wash your jars and lids. Sterilize your jars in a large pot filled with water. Bring the water to almost a simmer over medium heat. Keep the jars in the simmering water until you are ready to fill them. Use a jar lifter to remove them from the water when you are ready to fill them, dumping the hot water back into the pot when you remove each jar from the water. Right before you are ready to can, put your lids in a small pot or bowl with hot, but not boiling water. Put some additional white vinegar in a small bowl, alongside a clean washcloth or paper towel. Keep the water in your canning pot at a simmer while you fill your jars. See The All New Ball Book of Canning and Preserving for additional guidance

Combine apricots, lemon juice, sugar, and thyme in a glass bowl, cover and refrigerate for 4 hours or up to 24 hours. This macerating softens fresh fruit and draws out its natural juices, in which the fruit then soaks, like marinating. 

Gently bring macerated apricots to a boil and simmer, stirring occasionally, for 20 minutes until fruit is tender.

Add pectin stock to the pan and stir

Bring the mixture to a boil and gently boil, stirring from time to time, for 20 minutes or until a small dab of jam placed on one of your frozen plates wrinkles when pushed with your finger or until a sugar thermometer reads 220°.

While your jam is cooking, prepare your work surface On a clean cloth, lay out your jar lifter, bubble remover/lid lifter, funnel, bowl for lids in hot water, a bowl of vinegar, and clean cloth.

Remove the jam from the heat and place it on the trivet where you will be canning. (If you will not be canning the jam, fill your jars, allow them to cool, and then refrigerate.)

Using a jar lifer, remove one jar at a time from the hot water.

Spoon your jam into hot jars, leaving 1/4 inch headspace (1/2" if using Weck jars). Headspace is measured by laying your headspace gauge on the rim of the jar. In this case, have the notch next to '1/4 inch' laying on the rim of your jar. Your jam should just touch the bottom of the gauge.

Remove air bubbles and wipe the rim with vinegar.

Screw band down until resistance is met, then increase to fingertip tight. Fingertip tight is defined as tightening just with your fingertips, not needing the palm of your hand to tighten. (Or lay rubber gasket on the glass lid, place lid on the jar and secure with metal clamps if using Weck jars)

Place jars in large pot, making sure they are completely covered with water by 2 inches.

Cover pot and bring to a boil.

Once boiling set your timer and boil for 10 minutes.

At the end of 10 minutes, turn the heat off, remove the pot lid, and let sit for 5 minutes.

Carefully remove jars with the jar lifter and place them on a rack where they can sit undisturbed for 24 hours.