During night races, the heat is generally something that isn't worried about by many. With a 7:30 p.m. start time in Saturday's Coke Zero 400 at Daytona, the sun will likely not be too much of a factor. According to SB Nation's NASCAR weather expert, Brian Neudorff, most fans should expect "typical" Florida weather on Saturday.
When I say "typical" Florida weather, what I mean is mostly-to-partly-sunny days, hot with highs near 90 and humid. If you've ever been to Florida in the summer, then you know a spot shower or storm is likely at anytime during the afternoon. These storms leave as quickly as they form and are more miss than hit.
In Neudorff's weather report for the Coke Zero 400, he predicts that the temperature at the track will mostly be between 80-90 for the duration of the race.