just decrease the photo period by a few hours on the first day, then gradually increase.
for example: say your photo period is 10 hrs with the pc lighting you have now. put the t-5s on for 5 hours on day 1. keep it on for 5 hours a day for 5 days. on day 6, bump it up to 6 hours for another 5 days. at the end of that, then bump it up to seven hours, then eight, nine and ten, or until your back to your normal photo period.