Lithops seeds is extremely easy to germinate but can be challenging to grow on. The seedlings remain small and vulnerable for a couple of years. They require lots of sun but can quickly boil without good air movement to cool them off.

I like to sow seed in winter under lights. The tiny seedlings grow quite quickly to 1/4" or 1/2" in just a few months, with consistent warmth and water. I then adapt them to the spring sun, they produce their first true leaves and grow through the summer outdoors, and they are large enough to survive the winter without problems, then they produce their second true leaves in spring on a normal Lithops timetable.

Traditionally, Lithops seed were sown in autumn, as they would germinate in habitat. They would then grow through a sunny but cool and moist subtropical winter. In PA you would probably want to provide artificial light for the first winter. Lithops seeds germinate extremely quickly in hot weather but you will need to be especially careful to keep them moist during the first few weeks. Try growing them under plastic to keep the humidity up, but not in direct sun.

Here is a link that might be useful: Mesa Gardens for Lithops seed

i got a load of seed from cono's paridise in germany

Lithops seed are cheap enough where you can experiment many times until you find a system that works for you - the experience of trial and error is invaluable, the education is important in your understanding of these and other plants, and it can only encourage you to learn more and become a better grower as a result.

IMHO