Jeannine, ours started coming up volunteer at the same time tomato volunteers came up.
I started tomatillo seeds the same day I started tomatoes and peppers. But - Texas and Canada are a little bit different weather wise
Tomatillos germinate in soil temperatures between 65F and 85F. Most of the seeds I start indoors is in potting /starter mix around 75F - except for peppers - they like hotter temps.