I'm glad you noted the importance of having a regular time of observation. (wattsupwiththat.com)
My feeling is that these effects are all much smaller than the site move or time of observation biases that are being corrected for. (realclimate.org)
Consistent reliability of readings through quality of instrumentation and methodology - height, screening, correct times of observation etc. — could not be guaranteed until the advent of the Automatic Weather Station in the 1980's, but even then some of these have arguably been compromised by concerns over siting. (wattsupwiththat.com)