Its very hard and I have one who has to go out in a walking jacket and a lead with me, I have a busy road at front.
He ;ppls out the window and if its sunny he whines and whines.
Misa meows and shouts at me if I wont let him out, he cant get out of the garden any more but it drives me insane and dont like him going out in the rain cos his coat is just like a mop and he has arthritus.
Both cats do not go out at all in the winter, its hellish to start with but they get the idea eventually!
Sasa is the sensoble one, if its raining sshe wont go thro the door and in the winter doesnt want to go out............not bad for a semi feral whom lived outside all winter about 6 years ago, couldnt find where she was but neighbours down the road saw her. She was a real mess when she finally decided to come home.
I think you will have to be patient and endure the protests until he gets used to going out when you want...................getting him back will be the problem!
I have been out at 4 in the morning trying to find where Misa was hiding when its been a good summer and he still woudnt come in!