Creating good habits can take 28 days (at least), whereas breaking bad habits can take 1 second or 1 year, depending on the type of habit you're trying to break. Always correct bad habits immediately, as they can destroy everything you worked so hard on. Don't get down on yourself, just work hard to get those good habits back...the one's that kept you from the bad habits.
I smoked for 10 years and it took me approximately 3 weeks to almost "fully" quit, meaning mentally and physically. While I still caught myself craving a cigarette during memorable moments (hanging out with friends, etc), they eventually left 100% after a while. It takes a lot of patience, positive thoughts and persistence.
Just depending on what a bad habit you're talking about or habits you're talking about ? Take me for example it took me awhile to quit smoking but I did do it ? Why they quit they were making me really sick and headachey kind of it just I couldn't take it anymore? I guess whatever Habit you may have it just takes time everything in moderation all in due time To quit !
Not sure exactly, but you can Google that from experts. I've found it's important to replace the habit you are trying to break - and that takes approximately 40 days. I broke an addictive habit by joining a 12 step program, thus replacing the bad with good. I also started an abundance course which said it takes 40 days for the brain to really take hold of a new habit. Good Luck!