believe it or not I was once a butcher and that is a complex question. The no 1 issue is the quality of the edge, a good quality knife will be hard stay sharp and also have flexibility. There is no fixed time to sharpen a knife. First get a good edge with a grinder then give it a thorough steeling, then steel it before and after every usage, sometimes during. A new grind should not be necessary for several weeks if you know how to preserve and use a knife properly. We used only swiss victorinox.