... even if the day is warmer ...
I wouldn't worry too much about the OAT as that can be addressed by reduction methods. The problem is to do the tests with stable air, at dawn, and give yourself the best chance of getting reasonable numbers ..
Perhaps there's a job for me ..
.. and, if you find a job that requires less than 70-80 hours a week .. do let me know some contacts .. I could do with a semi-retirement job ..