If the soil is nice and damp, then now.

Thank you very much for your very prompt answer

Theses are not annuals, Geum, Penstomen and Echanacia are perennials and Lavender is a shrub. All of which should do well for some years.
I agree it will be alright to plant them out as long as you water them well in. The Perennials will need to be watered if it stays dry and perhaps protected from slugs? but Lavender dont like it too wet.