Is the white inside the wound an infection, and how long are wet to dry dressings needed? (Photo)

Great question! The area looks quite shallow, so there's not much to pack. I would recommend keeping it moist (with antibiotic ointment) and covering it with a dry dressing (bandaid). The area should heal by itself. The yellow at the base looks like granulation tissue, which is normal healing tissue.

The white that you are seeing is not a sign of infection in this wound.  Those signs would include pain, redness, and/or purulent drainage.  Deeper wounds heal from the bottom of the wound bed towards the surface.  In other words as it heals it will become less deep until it heals completely and is flush with the skin.  Continue to follow your surgeon's advice for the best outcome.

The white material in this wound is not an infection. Infection generally presents with a lot of redness and purulent discharge from the wound. When a wound heals, some dead tissue may present that should be debrided either by a knife or wet to dry dressings. These dressing changes will be used until the wound closes.