Hamsters can't resist some place to crawl into usually, so the ball is always useful even if they don't want to run in it. Most run like crazy in them though! Makes them faster from what I can see than just their feetsies alone, lol.....
By all means use a ball as part of taming, then maybe a bathtub. Most hams seem to freak out when we approach them inside their cage. They see it as THEIR cage, no one elses, the last place they can go and hide and store their stuff.
My first month with Ziggy, he never came out at all unless it was from cage to ball, and ball to bed, tub, or hand.....some don't get out of that habit. After four months now? I can almost lift Ziggy out of his cage by hand. Most of the time. Well, sometimes.....when he feels like it. Still haven't figured out why they follow things when they roll though....
LOL
Also, fifteen minutes is a good maximum for keeping a ham in a ball. Give them a cage, snack, pee break or the ball gets messy
Mine usually want to go right back to the ball once they had a sip of water.....
