I usually wait 8-12days after I've seen them sprout, by that time you might start seeing roots out of the bottem of ur drain holes which means time to transplant.
Also don't use nutrients yet if there still in Dixie cups, wait intel they have their second set of true leafs or intel u see just the littlest bit of yellow in the leafs, this means a nutrient deficiency and they should bounce back after adding some all purpose 20-20-20 (never start at full strength, try half or a quarter dose to start)
Hope that helps. Peace.