Water them deeply and thoroughly.
They are dehydrated.
All plants NEED sleep and/or a dark period every 24 hours to be able to complete their photosynthetic cycle, so by having had your lights on for 24/0 for weeks already, their metabolism is probably screwed up. Now that you have finally gone to 18/6, they will have to re-adjust and this may explain why the bud growth seems slow. Once they get back into the correct rhythm of light/dark/light/dark, they should get back into normal growth.
Regardless of what some people say or put out there, cannabis DEFINITELY needs an 18/6 light schedule to be healthy and functioing correctly and the myth that it is ok to grow cannabis (or any plant) for weeks/months without "sleep" is biologically incorrect and could only be recommended by people who either don't understand how plants function or do not understand how photosynthesis works, or perhaps both.
Hope this helps, Organoman.