The actual reason for giving a plant dark periods during Veg and Clone stages, i believe, and dont like hold me to this word for word cause im trying to pull up an obscue article i read a while back, but basically the apexial tip of the plant while the lights are on are getting the plants main focus of energy... ie. Sugars, but now when u switch the plants to darkness the apexial tip is no longer cause there is no light source to define where the apexial tip is. this in turn causes the plant to focus its energy on root growth and stalk girthing (Main Base) This is why i see no real problem giving early clones 24 hrs light, but once they start rooting i always give them atleast a 4 hr dark cycle. again just my preferance here.
I hope this is getting at the question u r asking.
Peace,
S i R