When to plant vegetables in Michigan Zone 5b?

I started my vegetables indoors two weeks ago. I've been growing them next to a sunny sliding glass door in my basement with supplemental CFL lamps. They have sprouted and have their first set of leaves and now I'm a little nervous. How soon can I plant them outside? Im hoping they will survive till end of April... but I'm not so sure... This is my first year planting and growing from seed indoors. I just did what they said on the back of the package.. ;)