What is the minimum time needed for force to move teeth and can it be done with fingers?

No, not with fingers: You cannot safely move your teeth with finger pressure. To avoid damaging roots of the teeth and the supporting bone you need constant, controlled, gentle pressure. This takes time because the bone has to dissolve on one side of the tooth and grow back on the other side as the tooth moves though the bone. This is why orthodontists have 6 years of dental training.

Instantly: As orthodontic forces are placed on the teeth, they start to move instantly. It is a slow process, whereas bone remodels as the teeth move. The brackets and wires stabilize and guide the movement. If you're asking if you can perform orthodontics on yourself with your fingers, the answer is no...you'll need the services of an orthodontist.

See an orthodontist: You don’t know what the dangers and implications are of attempting to straighten your teeth with fingers. The education, training, and experience are an extremely important part of being able to provide an orthodontic treatment. See an orthodontist for the best results.