um i do it when they get their second set of leaves. then i transplant the unuted soil into a hole of soil with more nutes like a a mix containing blood meal, bone meal, worm castings and bat guano
ive found the best thing to start seeds in is a mix of peat, vermiculite, and perlite i go with a 50% peat, 40% vermiculite, and 10% perlite. it works like a charm no nutes til plants get there 2nd set of true leaves
only cut the tips if your going to remove damaged parts or cut the whole leaf if its more than 2/3 dead.... theyre not that burnt so it doesnt matter to much