I plant the first set around the first of April.

Squash is a summer crop, not a spring crop. They like it hotter for sure which as farmerdill said may well be early April for you. For me it isn't until mid-late May.

Dave

I started mine indoors a few weeks ago. I have to grow them pretty big before planting because the snails love them when young.

The only problem with planting starts out too early is that they might simply sit there until warm enough. And if you have snails they will chomp them in the meantime :).

Squash and zuke seeds need to be pretty warm to sprout, so if you are direct seeding you need warm soil.