Can I switch from day to night lighting?

OK, 1st post here....great forum!...also 1st grow in Many years (think mid 70's), and 1st hydro/aero grow ever. I'm running a 18/6 schedule with lights on in the daytime, and I'd like to switch to nightime lighting to control the room temp better. These guys are now 3 weeks old from seed and seem to be doing pretty well, so I don't want to induce any undue stress at this stage. Can I shut down the lighting for 24-48hrs, and then start up with nightime lights?

If you shut down the lights for more than say 8 possibly 10 hours you are risking the plants building up hormones and starting to flower, more light less dark IMO would be the way to do this, leave them on for 22 or 24 and off for 4 or 6, until you have reached the timing you want. This will cause less stress and likelyhood of flowering early. Looking good, good luck.

Keeping the lights going longer, and just slowly "shifting day to night" makes sense...I may be trying to cure a problem that does'nt exist though....night temp is 66° (with supplimental heat) and day runs 75-77° . If I reverse the lighting to nightime, I could eliminate the aux night heating.

I personally prefer a night cycle, works better for me, can still work a full time job, spend time with the kids and wife, and garden at night. It is winter here, don't know where you are, so temps don't matter so much, but in the middle of the summer when outside temps are 90-100 its a bitch to keep the 1000 watt on and the room cool during the day.

Thanks for the input, it so happens I am in the Mile High State myself, but grow room is in the basement, but it is still 72-74° in the summer down there WITHOUT any lighting....sooo I may try the switch, even though this grow will be over by the end of March or so.