Advice on switching on/off times for seedlings already on 12/12

I am doing a 12/12 from seed experiment and my existing light schedule is on at 5:30 PM and off at 5:30 AM. My situation has changed and I now need the light to go on at 10:00 AM and off at 10:00 PM.

The seedlings are approx 10 days old, between 1 and 2 inches tall and are just putting out their 2nd set of real leaves. If I make the switch all at once, they will have a 12 hour dark period followed by 4 1/2 hours of light followed by another 12 hour dark period before being on the new schedule.

Is there risk of doing harm? Should I try do this switch gradually like having 12 hour on, 13 hour off until I can get to the new schedule?

Thanks!

Do the change at once. The plants will be fine. The fewer times you adjust the light cycle the better.

That's what I was hoping...thanks man!

I concur with @HighLife4Me. I've had to do this a couple times in the past (once in my 12/12 from clone run, much like you're doing).

No harm done as long as you're not doing it often.

-spek

Cool, thanks. Hopefully this will be the one and only time. Since they are so young I was kind of figuring it would be fine but I wanted to ask you all. I can't wait until I can obtain membership status so I can start my journal.

I have been forced to do this several times over the years. I usually go 24 hours straight darkness or however long it takes to get my schedule back on track. I have never had ill effects. If you are trying to sex your seedlings, the extra dark period will induce flowering even more.

Thanks guys. All my seeds were fem seeds to begin with so I guess that did not matter. I went ahead and made the switch last night and am now on the new schedule.