Menstrual cups in for 12 hours?!

So I've been considering getting a menstrual cup as everyone says they are great and you can keep them in for up to 12 hours, I was just wondering if that is possible on heavy days as I know I have to change my tampon every 2-3 hours on my heavy days but 12 hours with a menstrual cup?! Tell me your experiences with them please ladies.