I've never grown herbs to that height under lights (they go outside as soon as possible), so I'll let others chime in.

BUT, they will not grow at the same speed. Parsley is always slower to germinate and get going for me. Also, I would recommend removing the heated mat after the seeds germinate. You will then have to figure out how to keep the air warm enough to speed up growth, and not cook the roots.

What's your fertilizing plan?

Parsley (once it comes up) and basil are pretty fast, if it's warm. I think oregano is a lot slower. See how long it takes to be 1", and then multiply by 6! Growing speed is strongly dependent on temperature. Without knowing your temp, I wouldn't hazard a guess.

They don't all grow at the same speed. Dill is a tall plant and oregano is a spreading low-grower.

After sprouting, don't leave them on the heat mat. And seed starting X weeks before last frost guides can help. Not only helpful for frost, but also a good point of maturity for transplanting- but not yet big like 6" growth yet.

Oregano is the slowest- it's 6-10 weeks before last frost, but it grows slower than parsley. Many parsley type are around 8-12 weeks, but they plush up faster than oregano once they get going. Dill next, with a couple weeks before setting out. Basil can go pretty quick, but that can depend on the variety- a week or two. Chives is the quickest, and is so fast it is sometimes used for micro greens.

How fast your seeds get from germinated to mature enough to transplant out to 6" tall depends a lot on what variety, your lighting, heat mat and air temp after you take your seedlings off the mat, feeding and watering...

You might get 6" off dill, basil, and chives in 10 weeks depending, but not likely with the parsley and oregano in 10 weeks.

Dill doesn’t transplant well, if that was your intention. It’ll bolt as soon as look at you. Parsley isn’t that keen on it either. Basil couldn’t care less and chives and oregano, being perennial don’t mind either.

Thanks! I know there is a variance but I wanted some best guesses which I got.