I was 5 weeks into flower and looked like one plant was locked out with leaves yellowing and rusty spots all over them.
I flushed with tap water while I was moving shit in my tent I inadvertently clicked my timer off and the plants were 6 days under 24 hours light.
How bad?
if it starts growing new leaves, it's not good... it may still pop some extra nanners even if it avoids re-vege.
it's about a hormonal balance, and as long as you didn't shift it back too far, it is mostly fine.