I would leave them indoors until you return. Choose a well lighted location, out of direct sunlight. Provide some indirect air circulation if possible, ceiling fan maybe? Water them just before you leave.
Wait until true leaves appear before placing outdoors, then place in a shady location for a few hours each day for about a week before leaving them outside. Be sure to protect them against being uprooted by curious animals, squirrels, chipmunks, etc. with wire netting.
It is advisable to handle the seedlings by the leaves only during transplanting, as the stems and roots are very tender and may become bruised, which can cause failure of the plant.
I prefer to wait until they are at least 1½-2" tall before transplanting into individual pots and then 6" or more before planting in the garden. If I have a color mix, I will often grow in pots until they bloom before selecting ones to plant.
I now have 2 trays of mixed color doubles and yellow flowering ones on a shaded porch becoming acclimated to the great outdoors before planting. Some are large enough to transplant, but am waiting for the rains to return (hopefully, one of these days!) and temps to cool down somewhat.
Enjoy your vacation!
Rb