Light change from 24 hours to 18-6?

I have a question that I hope someone can help me out with. I have had my light set to 24 hours from seed, to almost three weeks old. I was using a timer for 18-6 for 2 days then it broke. So I just left the light on when I was at work. So is that going to mess with the plants ? Is it ok to switch back to 18 -6 after I get a timer ??

They'll be fine.. as long as you don't go below 18/6.... what kind of lights though? HID's do well on 18/6... but for floro grows 24-hour light is almost a must! The intensity just isn't there- unless using T5's