Is it ok to leave adult dog alone for 10 hours M-F ?

I am considering adopting a medium sized adult dog, but will have to leave him alone 9-10 hours a day. He'd been in a bedroom with a doggy door to the yard. Id exercise him a bit (maybe 15- 20 minutes) each morning, and spend time with him every night and on the weekends. Is 9-10 hours too long to leave an adult dog home alone? I've done some research and the responses are pretty mixed. Some say as long as you leave on the radio or leave him with stimulating toys/treats, he'll be alright for 10 hours alone. I mean, some days my stepmom might drop by the house during the afternoon, but for the most part the dog would be on his own M-F. I very much want to rescue a pooch but feel guilty about the hours hed spend alone. Any advice would be greatly appreciated.