put a light coating of worm castings on the seeds. it helps prevent dampening off. has greatly reduced my loses. a heat mat until they germinate helps as well. just started creeping thyme last t week and all germinated.
Try the species sold as “Mother Of Thyme”. It has more vigor than the others and in my opinion a better taste.
To propagate small seeds, fill a seed starting tray or plug tray with drainage to the top with seed starting mix, then gently spray it with a hose (or in your bathroom shower) until the soil is about 3/4 height from full. Then place the seeds on top of the soil. Finally cover the seeds with an 1/8" to 1/4" of vermiculite (not perlite) and mist the top – preferably with a 16-24 fl.oz. plastic spray bottle. Place the tray away from direct sunlight until the seeds sprout. Mist the vermiculite about every 8-12 hours so it doesn’t completely dry out. Do not let the soil tray sit in water. Water that drains out can be caught in a nursery tray but discard it daily. Placing them on a heat mat with temperature probe in the soil set at 73°F will speed propagation.
Thyme and most herbs hate fertile soil. Start with coarse sand and add some peat moss to improve moisture retention. Provide no nutrition until they are well established. Even after that compost is about all you will ever need.
Directly seeded mother of thyme in the sand between my paving stones. The picture was from last year when I was still worried about bare spots now I have to mow it.