Usually 8-10 hours is good. They do need 10-12 hours of uninterupted darkness though so 10 hours is what I'd call max. My lights on are from 8am to 8pm.
Root tabs are super easy, I actually break mine in half and you push it in the substrate, you can follow the directions on the package or you can just put half under the sword and then put the other half under it a month later when it dissolves. They are slow dissolving fertilizer, hence it's good for amazon swords
I break mine in half an I've got two swords so each gets a half for a month and then I check to see if it's dissolved and replace it if it is ^_^