To harden-off, simply gradually increase your plants daily exposure to conditions outside. Ideally, this means on day one just a few hours outside in a semi-shaded and sheltered area, with increased hours on days two and three. By day four there should be more direct sunlight and exposure to wind, and so on, until by night six the plants are spending the night outdoors. However, the reality is that most people do not have the luxury to hang around until mid-morning, when the cool of the night has passed, simply to put out trays of seedlings. And those people who begin working at noon can scarcely rush home at 4 p.m. to bring in the seedlings.
Some creativity is required.
Start hardening off your flowers and vegetables on the weekend. That way you'll be around for the first two, most fragile days. On day three, control either wind or sun by putting up a windbreak or a sunshade. That way the seedlings are not coping with both elements at once for your entire workday. The next day alter which element they are coping with, until day five when they are on their own.