how long can seedlings stay in dixie cups?

I planted them in plastic cups. How long till I have to transplant them?

well if they are clear cups, wait until you can see the roots bound and start wrapping up the sides about 2 inches or so. if they arent clear, poke a few holes in the bottom and wait til a taproot makes it out. thats what i would do.

I started a bunch of plants in 4x4" square pots and I transplanted those at about 2 weeks. Let them get a chance to make some roots then it's time to go. I started another in a 6" round, since I ran out, and that one is doing way better than the rest. It's actually a weird phenotype so I don't know for sure if it's the plant, or being started in the bigger pot, but next time I'll be starting more in 6" round containers.

If you'd like you can gently slide the dirt out to inspect the rootball before moving up. I do this often myself but find few other people do. Again, just be careful if you do.