About the open soffit, I think it's been open long enough, that if he wanted really wanted to leave, he would have taken the risk and jumped by now.I’m afraid to have him go out and like it and then not to be able do during the day - which could make the open soffit more attractive.
But about opening the catio at night, my only concern is that he will love it out there, and not go back in the shed in the morning, when you need to run the air conditioner. Does the sun shine on that side of the shed, and if so, is there anything to give shade in the catio?