It seems the best time for me is a few hours into the morning especially if it is sunny or a few hours before it gets dark. My reasoning for this is in the morning the track will have heat in it to help with traction and the air temp will still be reasonable. Then the pre-evening time is when the sun / radiant heat is lower but the track still has heat in it from the day.

This was our logic back in our Sprint car days.

Now if you can find a bright sunny day with cool (60-70) air temps watch out ! The track will usually hold all day.

The worst (for me anyway) seems to be from noon till 4-5 p.m. and night time. During the mid-day tiimes the track seems to get greasy from to much heat and the evening tend to be greasy as well because of no heat.

Now if you car does not depend upon 60ft. times (insert bad 60ft. cars here) then I would venture to say a cold night would be perfect.