It's called re-vegging. I have a thread on it. Depends on a few factors but if we're talking clones, expect normal growth in roughly six weeks on 18/6 (or your preferred vegging light schedule).
YES they do! My strong OG mothers only had 3 leaves as seedlings. Then grew regular. Took 6 clones off each plant in veg. Then all the new growth on clones was 3 leave for a few weeks. And they eat me outta house n home on nutritions too. Clones that WANT around 1200ppm?! Yehhh lol