Depnds on th cell size. If small, the risk is high as to root damage during transplant. Heat mats under seed sprouting trays is helpful in getting faster growth. Also, plenty of light under fl tubes at about 18 hours per day. There are mild fertilizers used for seedlings. Slow growth? how long has it been since planting oregano? In Z8 it might be just fine to direct plant outside. Usually, I plant seeds in 2 inch pots at the beginning and the plants remain in these until they get moved and transplanted directly to the garden. I don't use the tiny cells for anything.

Here is a link that might be useful: PHC fertilizer for seedlings

Hi, not sure about the separating but I would agree that yes, thyme is not as hearty as some other seedlings. Recently I did basil, lavender, chamomile, and thyme all from seeds and the thyme is the most fragile. Even now the stems are growing nicely but get easily knocked over if I move them or water too fervently, etc. But then, thyme is a delicate plant compared to others.
Secondly, regarding the direct seeding quetion, I start all my seeds directly outdoors, in small pots (2 to 3 inches), with just some good potting soil and sometimes a little gravel on the bottom. I have very good luck this way. Of the plants you named, I have done this successfully with sage and thyme. Never tried the others. I would imagine that it depends a lot on your climate (I'm in Los Angeles).
Let us know how it all turns out, there's something to be learned here!!

Odd, my thyme was started from seeds two years ago and I still have two big clumps of it still growing. Its now got lots of dead oak leaves caught in it, they are easy to remove. Its survival through winters prove to me its quite hardy. Right now, because its winter and it was under 2 feet of snow, the leaves are a very dark green black color. It should lihten up once it gets warmer outside.

I've direct sowed thyme, sage, parsley and chives with good results. I'm going to assume that I'm much farther north than you since you are a zone 8 while I'm a zone 5/6. I only need to water plants here when it has been exceptionally hot and dry. If you get very hot or dry summers I would take the extra time and effort to watch and water these young plants as needed. Once they establish themselves, thyme and sage like it on the dry side but young plants are different. Good luck!

FataMorgana