I had to wait about 2 weeks in between sessions. You need it to heal before you can do fill in and colors. If it scabs, it can rip out some ink and make it look blotchy and bad. Also you want to make sure the swelling goes down fully. Black outline work isnt too bad. Its when they use the color fill in needles, thats when it starts to hurt as those things are like 4 needles all grouped together and they just have to grind it into the skin so they get plenty of ink in there. Also it depends how much pain you can take. Most artists will ask if you are ok. My artist didnt want to do longer than 4-6 hour sessions not only for his own sanity but also for the customer lol.