Once the seedling has been planted into it's own pot, it needs about a week of greenhouse care to grow new roots. Then they could be placed outside (still in pots), assuming the weather is not too hot or too cold. Hot =80 degrees cold =45 degrees.

Well I know folks use the wintersow (actually springsow) method to start their Dahlia and plant them directly from sowing container to ground just fine. That potting them up for a week step is skipped. We winter sowers like to transplant our seedlings (no matter what) from sowing container to ground when seedlings are just barely in the 2nd true-leaf stage or smaller. Sometimes however certain seedlings (species depending) are exceptionally yummy to certain pests (slugs, ect) and they do get potted up and planted out later as bigger robust plants); it just depends.
Since you didn't use the method above (see winter sowing forum) you will need to harden them off by giving them a little more sunlight gradually over a week to 2 week period. The first day start them off in the shade then move them into sun for a short period and them make it a little longer each day until you can leave them all day and all night outdoors. That is hardening-off :)

Good luck

I would not leave them out yet. 36 is too close to freezing. I have a few days right around freezing that killed brand new store bought, very healthy and large tubers. Not a single scrap of tuber to be salveged!

All it took was one night to ruin my tubers!

What I would do, is watch the weather closely, put them out during the day, this will save you window space / lighting space indoors. Let them bask in the sun all day (gradually work them into the sun). But, you are going to need to bring them in during the night for nights forecasted below 45. Not fun, but important.

Better safe then sorry.

I am in the process of hardening off my dahlia seedlings and I appreciate all this good advice! Thank you.