Answer: Since these are still seedlings you risk their demise from frost. If they were full grown there would be no problem, but they're not. They really need to be "hardened off". By this we mean that they need to be gradually toughened up for transition to the garden. If you don't do this the tender leaves will probably be damaged by temperature, sun or even wind.
Is it possible you could rig up a cold frame or other protected area? You could them put them out for part of the day, gradually increasing their time outdoors over the course of about a week. I know this isn't helping you make more room for seedlings inside right away, but it would be awful to lose all the ones you've already worked so hard on!
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