I don't think it would hurt the plants.... Your yield will be reduced though....

Think of it like direct and indirect sunlight....the 600w being direct intense light, and the floros as indirect lighting.... It's the total time of light period that will make them flower so doing this shouldn't cause too much stress....

It would be best to find a way to control temps in your grow area.... Got an A/C register in the room??? If so, you can easily extend it into your tent, if you don't already have that going....

After all, you didnt get yourself that 600w to just end up turning it off halfway during light cycles....find a way to control temps so you can take advantage of what you have available to you....

Hope this helps....

CGI::::::