This is light stress.
20hrs is FAR to much DLI..
Autos work of energy bursts. As do most living stuff
Think, us humans staying up 20hrs a day every week. And then going about our chores. Now, add 4hrs of extra sleep to that same persons weekly sleep. Or even 6-7. That person can work harder, more productive etc.
ITS THE EXACT same with plants
They're droopy. Because they're exhausted. (The question about should you continue, EH, YE, Why would you not)
Rightly they can finish on 20hrs. But in order to do this. You need to change the light %. But simply by giving them 6-8hrs of dark rest. Will fix the issue within 72hrz.