Time depends on how black you want the blade and how deep you want the etch. I haven’t worked with Damascus much but I believe on this blade I did three or four rounds of about five minutes each. The blade was hand sanded to 800 grit then etched for five minutes. The blade was sprayed with Windex to stop the etching process. Don’t spray the windex around your etching solution. It will kill it. It was washed in hot water and dried after each round. After the etching process it was hand sanded again with 800 grit to bring out the silver. Some guys also soak the blade in coffee after etching to make the black, blacker. I haven’t tried that yet. Maybe on my next one. There are some very good YouTube videos that explains the process better than I have here.