This is the most annoying, widespread and unforgivable mistake in all online erotica, not just SOL. I think it comes from spelling out of nasal pronunciation.
Then is about time: Then it was time to go.
Than is about comparing: Mine is larger than yours.
A trick to keep them apart:
-- then and time have a letter "E" in them;
-- than and comparison have a letter "A" in them.
Please, please keep these straight. I am a volunteer proofreader/editor with professional experience.