I doubt it's too late. I'd start putting it outside on 60 degree days, then taking it inside (or put it in a garage) if it's too much of a drop at night. Gradually lower the temps it's exposed to if you're worried about shocking it too much.

No problem at all with taking it directly outdoors - that's where it needs to be. Maples are NOT indoor plants. If it drops leaves, fine -- maples will be going dormant soon anyway.

If you have concerns, place where it will be out of direct sun. And you will need to sink the pot completely into the soil to protect against root damage during winter cold. You can unpot and plant permanently in spring.