A perianal abscess wound healing time will depend on the size of the abscess cavity as well as whether the abscess is associated with an anal fistula.
Generally, an abscess that is smaller than 2cm in size heals within 2-3 weeks. An abscess large than 5cm may take 4-6 weeks to heal. It is important to wash your buttocks frequently to keep the area clean.
Cleaning yourself with water (such as using the shower spray) after bowel movement helps keep the wound clean from faeces. That is important to allow the wound to heal quickly.
If you find that the wound does not heal completely in 6 weeks, you may be suffering from an anal fistula. You should consult a colorectal surgeon in that case to confirm the diagnosis and get the fistula treated.