Not very much unless there is a huge change but generally richen the hsn a fraction if it gets hotter and lean it if it gets colder.However in 20 years racing I don't think I've ever had the conditions change so drastically in one day that I've had to really retune..Methanol burning engines do like cool early mornings with plenty of humidity though so a day that begins cool and damp then dries out and gets very hot in the afternoon might certainly mean running a tad richer later in the day.

edit..reverse that..teach me to type while stoned...richen for cold/damp weather and lean for hot dry...sorry