You will get better hp and tq number if you were to tune it during the winter. But it you were to tune it during the summer the dyno should be able to give you a correction factor to a standard day.
www.thetuningschool.com sales, support, research and tuner
2008 Corvette A6 1 7/8 kooks catted headers, air raid intake, ported TB, NPP exhaust and tuned with HP tuners. 425hp/428tq