I do the same as Kay Jones, mostly because here on Cape Cod we have a long slow Spring. Some of my WS "babies" have true leaves today, but I'm not going to plant them out because it's still too cooooold --and going to be down in the low thirties at night for the next few days. I'll actually wait several more weeks to plant out. Seems REALLY long, :-( but in two years of WS, I've discovered that my WS seedlings catch up really fast once the soil warms up in early June.
I start planting out perennials and hardy annuals as soon as I think they're *ready* and I can find time. For me, ready = any time after they have one set of true leaves. I planted out California poppies and digitalis this week, didn't get time for any more. Laura Bush petunia is past ready too and it will go out next, as soon as time permits.
I don't plant out tenders, like zinnias, until around mid May, when there's less chance of frost here.
But I did sow 6 more jugs today- zinnias, nasturtiums, and castor beans.