I would suggest you ask to Zhu Fen, Huazhong Agricultural University, China. https://www.researchgate.net/profile/Fen_Zhu
She has reared this fly in various controlled conditions as part of the PROTEINSECT project (http://www.proteinsect.eu/) . But these temperatures are probably close to the lower temperature development threshold and, so, it is not easy to determine.
You can take a look at this article - Temperature adaptation in Chrysomya megacephala and Chrysomya pinguis, two blow fly species of forensic significance. Shih-Tsai Yang andShiuh-Feng Shiao, Entomologia Experimentalis et Applicata, Volume 152, Issue 2, pages 100–107, August 2014.
And at the articles attached, if you don't have them already.
Why dont you extrapolate data from your previous experiments... cause data from other workers might not suit the conditions prevalant in our country, that is if your doing feild based analysis.