If you have him in minute-long stays already, then it sounds like you're doing something right! If his previous owner didn't bother training him, it could be that he's also had limited opportunities to experience new and different situations.
He'll get the hang of it eventually
He sounds like a great little fella!
Good luck with your training sessions! Milly had a couple of different trainers before we finally settled on one who was suitable. She was his first Yorkie, but his methods really worked for Milly.