Hey CocoGrow, go easy on the nutrients they are only seedling and if you have nutrients in your soil don't supplement just yet until they have grown a little more. As far as time when to transplant will determine when they've outgrown the solo cups. No one can tell you when that will occur as it depends on how long it will take. One thing for sure you don't want them to get rootbound in the cups therefore we you see a solid root base at the bottom then that's your cue. Hope this helps, Cheers.