If the keycaps are blank, it takes some time, as everyone else says. But it takes even longer if the keycaps are cherry profile because, at least from my experience, those wire keypullers can dig into the keycaps and dent them. So if I am swapping out cherry profile keycaps, I usually use the wire keypuller for the 1x keys and then floss for the 1.25, 1.5+ size keycaps. That takes a lot of time, I have not timed it but probably 25 mins if they are cherry profile.