I am guessing these seedlings are in a container and not planted in the ground? If so, they might need protection if temps drop low enough.....JM roots can be damaged at 25F. Otherwise, they could just be left outside with a decent cover of mulch. Just keep an eye out for any serious cold snaps.

I'd wrap the container with a clear plastic bag (Home Depot, clear large leaf bags). Keep it slightly open at the top. Use sticks if you don't want it to collapse from the wind.