Yes, it's too early, specially as we're having lower temperatures than usual for May. End of May is the recommended planting out time for summer bedding, possibly later in the North by a week or two - all risk of frost must be past.

I'm planting what I can in easily moveable tubs and bringing them in at night --- tedious!--- the rest will have to be hardened off and planted out later

Ive had my Calendula plants in the border for weeks now, they have their first flower buds starting to show, all grown in the greenhouse,

Calendulas are hardy annuals, Peedee, not half hardy like most summer bedding.