The last frost date in my corner of the universe is May 10th. Daily low temperatures are above 5C/41F for at least the next 14 days, according to the forecasts (which are still reliable here in Canada).
We’ll be moving the tomato plants, bell pepper plants, eggplant plants, marigold plants and zinnia plants outdoors. (The squash/zucchinis/courgettes will likely wait for a little bit.)
Every expert gardener will tell you to bring the plants outdoors for short durations to slowly acclimatize them to the sun, the wind, the temperatures. If you don’t do this, you risk transplant shock and could possibly kill your seedlings.
I’m extremely lazy and I usually take the risk. We transplant on a rainy day, preferably the start of a series of rainy days. We have spare plants just in case. And we hope for the best.
(knock on wood)