Dentists say twice, I floss once in the evening after I’ve stopped eating, and at other times if something feels stuck in my teeth.
Without being a dentist, or dental hygienist, my best guess would be to floss at least twice a day... But ideally after eating, and especially if you have eaten meat or have any food lodged between your teeth.
At least two! But I think dentists suggest that it should be done after every meal. I carry a couple of floss picks in my purse in case I eat out.
You should floss often, at least once a day. I try to do that. My teeth feel so clean when I floss and then brush. Floss correctly for max impact.