Just because he is confident indoors doesn't mean he will be outdoors. He's just moved from one home to another, he won't be used to your house yet, life where is the only cat, and putting him outside and leaving him there isn't going to achieve anything except frighten him. Not all cats like going outside. Some cats prefer to be lazy and sleep on the sofa all day and play all night. They're all different, just because it's "normal" to put a cat outside and leave them there doesn't mean that all cats will tolerate it.
And you asked for "advice" so people gave it to you.