Yes wait until all threat of frost has passed.

It does depend a bit where you are. Here in the south west and close to the sea, I'm not expecting any more frost. You could start the hardening off process on days that are not too cold. Put the plants outside in a sheltered spot for a while, increasing the time spent outside and the exposure, but bringing them in at night. Gradually acclimatise the plants to being outside over a couple of weeks and see how the weather is at the beginning of May. If the risk of frost is over they can stay out overnight as well.