I don't think you need to do anything too intense like this ! I was doing 30 sit ups a day and then built it up to around 50 a day and my girlfriend was like damn just look at your abs. I never walked around with no top on as I am not about that life. I would find it hard to keep changing into different exercises like that, plus you can do sit ups at your own pace and even spread it out if you have to throughout the day :).