What happens if I seal my driveway on a cool day and then it rains?
From Blackjack 500 technical manual:


  Temperatures must be 65°F and rising, but below 90°F during application. Clean driveway with
  Drive Kleen and thoroughly rinse. Remove puddles and then apply sealer to a slightly damp surface
  (not wet). A small amount of water separation in the pail is normal, and should be easily
  mixed in. Pour out 1/3 of the container and spread product across the blacktop surface with a
  squeegee. Squeegee must be used to spread product and for proper application rates. After
  application with squeegee, a follow up with a brush may be used if a textured surface is desired.
  Complete the entire driveway in one continuous application to prevent “color shading”. If multiple
  pails are used, it is best to match batch codes and blend the end of one pail into the beginning of
  the other to maintain consistent coloring and texture. Do not over apply as this may lead to track- ing. Do not apply if rain or cold temperatures are expected within 36 hours


As implied by @Daniel Griscom, you really ought to read and follow the directions on the product container