glum:
If you're asking whether the temperature at typical jet cruising levels varies according to whether it's night or day then I'll offer my own observation. No, not that I've ever noticed. Temperature variations at typical cruising altitudes are attributable to upper air pressure patterns and the associated meandering of the jet stream. Large variations in temperature aloft are often noted in the vicinity of large frontal systems and convective activity.
Understanding the complex nature of climate and meteorology is a lifelong pursuit consisting of specific education, training and continuing study. Pilots with a basic understanding have a unique opportunity to compare the standard atmospheric models they've become familiar with through training to what they see while flying their aircraft. It is a highly interesting pursuit that I try not to confuse with the actual scientific understanding possessed by actual meteorological experts! But I hope your question has been addressed.
westhawk