Answer: When they're good and ready.
I still have eggplants coming up. What... fifty+ days later? Off course at this point I have no idea what kind they are. I'd given up on them and reused the pots for transplanting doubles. So now I'm digging them out of those pots and transplanting them into other "failed" pots. At first I thought they were peppers but some of them are putting out little round eggplant leaves. So we have half a dozen Mystery Eggplants to give away. I'll keep a couple myself.
The second batch of tomato seeds in the cold frame are coming up as are my okra. I have two flats of nice cucumbers, and melons. The nematodes have been applied to the beds, the lettuce have been transplanted and the peas are doing great.