How long will I need to be on low-dose (20mg) Accutane for cystic acne if I am a 165 lb male and I get 1-2 small cysts a month?

I’m 165 pound male and I have received a rx for low dose 20mg accutane/day for occasional lower face cystic acne (maybe 1-2 small cysts/month) but when I do get them they can leave scars and take a week to resolve hence why I asked for accutane. How long must I remain on accutane? I would like to take the lowest possible dose which will still give long term results. Btw I was already on accutane regular dose when I was 15. I was acne-free for 15 years. Thank you!