Normally third week of May is when last frosts happen - so now. I have had them in since April due to the warmish weather.

blimey, optimistic there Kildermorie - we've had frost in London on 4th June before, so the usual advice is end of May for summer bedding. Depends where you are though, would have helped if you'd said - I've had my summer bedding out in a sheltered spot for 5 days already here in London, but wouldn't recommend it in the north, for instance. Geraniums should be fine even with a light frost, its the busy lizzies that'll keel over at the first hint of it.