Think of it this way - hardening off developed plants means they have to be gradually, over several days and for brief periods of time, exposed to the very different environment of outside. First in the shade and only slowly exposed to the sun and wind vs. where they have been - indoors under light.

So if they are still small seedlings (not well developed plants), and you haven't "started hardening them off yet" then what are the odds of them surviving if you put them cold turkey "outside in the sun on nice days for a couple of hours"? Almost nil.

Outside temperatures, wind, and sun are not friends for young seedlings unless they were germinated and grown in those conditions OR unless they are mature enough to begin carefully hardening them off in heavy shade.

Dave

You can look for small portable greenhouse, that is usually sold for about $20 at stores. It is flimsy and needs to be tied down to the wall or railing but has few shelves and does the job of helping with hardening