Oh the difference one tiny vowel makes. Some things just shouldn’t be set in stone … or allowed to dry in cement. Dr. Grammar explains it well (despite his affection for golf references):
Than is used to indicate comparison or degree.
Example: His drive was longer than mine.
Then is used to indicate time.
Example: Then he putted out and won the tournament.
Don’t confuse the two. (Please; I’m begging you. Don’t. It bothers me.)